Method for producing α-L-aspartyl-L-phenylalanine-β-ester and method for producing α-L-aspartyl-L-phenylalanine-α-methyl ester

ABSTRACT

A method for producing an α-L-aspartyl-L-phenylalanine-β-ester (also named α-L-(β-o-substituted aspartyl)-L-phenylalanine), which is an intermediate of an α-L-aspartyl-L-phenylalanine-α-methyl ester (also named α-L-aspartyl-L-phenylalanine methyl ester; product name: aspartame), easily, at high yield and inexpensively without going through a complex synthesis method is provided. Further, an easy, inexpensive and high-yield production method for an α-L-aspartyl-L-phenylalanine-α-methyl ester is provided. α-L-aspartyl-L-phenylalanine-α-methyl ester is produced from a L-aspartic acid-α,β-diester and L-phenylalanine using an enzyme or enzyme-containing substance that has an ability to catalyze a reaction in which L-phenylalanine performs no nucleophilic attack on a β-ester site of L-aspartic acid-α,β-diester but performs a nucleophilic attack on an α-ester site thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Ser. No. 10/876,673, filed on Jun. 28, 2004 now U.S. Pat. No. 7,361,458, which is a continuation of PCT/JP2004/000620 filed on Jan. 23, 2004, which claims priority to JP 2003-016764, filed on Jan. 24, 2003, JP 2003-201819, filed on Jul. 25, 2003, and US 60/491,546, filed on Aug. 1, 2003.

TECHNICAL FIELD

The present invention relates to a method for producing an α-L-aspartyl-L-phenylalanine-β-ester (also named as “α-L-(β-o-substituted aspartyl)-L-phenylalanine (abbreviation: α-ARP)) and to a method for producing an α-L-aspartyl-L-phenylalanine-α-methyl ester (also named α-L-aspartyl-L-phenylalanine methyl ester (abbreviation: α-APM). More particularly, the present invention relates to a method for producing an α-L-aspartyl-L-phenylalanine-β-ester, which is an important intermediate for producing an α-L-aspartyl-L-phenylalanine-α-methyl ester (product name: aspartame) that is in great demand as a sweetener, and to a method for producing an α-L-aspartyl-L-phenylalanine-α-methyl ester utilizing the method for producing the α-L-aspartyl-L-phenylalanine-β-ester.

BACKGROUND ART

Conventionally known methods for producing α-L-aspartyl-L-phenylalanine-α-methyl ester (hereinafter, “α-APM” for short in some cases) include a chemical synthesis method and enzymatic synthesis method. As the chemical synthesis method, there has been known a method for condensing an N-protected L-aspartic acid anhydride with L-phenylalanine methyl ester to synthesize an N-protected APM and eliminating the N-protecting group to obtain APM, and as the enzymatic synthesis method, there has been known a method for condensing an N-protected L-aspartic acid with L-phenylalanine methyl ester to synthesize an N-protected APM and eliminating the N-protecting group to obtain APM. In both of the methods, however, steps of introducing a protecting group and eliminating the protecting group are necessary and the processes are very troublesome. On the other hand, an APM production method in which no N-protecting group is used has been studied (see Japanese Patent Publication No. H02-015196 Gazette). However, this method is not suitable for industrial production due to very low yield of the product. Thus, under such circumstances, development of industrial production methods for aspartame at lower cost has been desired.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a method for producing an α-L-aspartyl-L-phenylalanine-β-ester, which is an intermediate of an α-L-aspartyl-L-phenylalanine-α-methyl ester, easily, inexpensively and at high yield without going through a complex synthesis method. Further, it is an object of the present invention to provide a method for producing an α-L-aspartyl-L-phenylalanine-α-methyl ester easily, inexpensively, and at high yield.

As a result of conducting extensive research in consideration of the above objects, the inventors of the present invention have found that a newly discovered enzyme or an enzyme-containing substance is capable of selectively producing an α-L-aspartyl-L-phenylalanine-β-ester from an L-aspartic acid-α,β-diester and L-phenylalanine, and have achieved the present invention.

Namely, the present invention is as described below.

-   [1] A method of producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine), comprising     forming the α-L-aspartyl-L-phenylalanine-β-ester from L-aspartic     acid-α,β-diester and L-phenylalanine using an enzyme or     enzyme-containing substance that has an ability to selectively link     L-phenylalanine to an α-ester site of the L-aspartic     acid-α,β-diester through a peptide bond. -   [2] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [1] above, wherein the enzyme or enzyme-containing substance is one     type or two or more types selected from the group consisting of a     culture of a microbe that has an ability to selectively link     L-phenylalanine to an α-ester site of the L-aspartic     acid-α,β-diester through a peptide bond, a microbial cell separated     from the culture and a treated microbial cell product of the     microbe. -   [3] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2] above, wherein the microbe is a microbe belonging to a genus     selected from the group consisting of Aeromonas, Azotobacter,     Alcaligenes, Brevibacterium, Corynebacterium, Escherichia,     Empedobacter, Flavobacterium, Microbacterium, Propionibacterium,     Brevibacillus, Paenibacillus, Pseudomonas, Serratia,     Stenotrophomonas, Sphingobacterium, Streptomyces, Xanthomonas,     Williopsis, Candida, Geotrichum, Pichia, Saccharomyces, Torulaspora,     Cellulophaga, Weeksela, Pedobacter, Persicobacter, Flexithrix,     Chitinophaga, Cyclobacterium, Runella, Thermonema, Psychroserpens,     Gelidibacter, Dyadobacter, Flammeovirga, Spirosoma, Flectobacillus,     Tenacibaculum, Rhodotermus, Zobellia, Muricauda, Salegentibacter,     Taxeobacter, Cytophaga, Marinilabilia, Lewinella, Saprospira, and     Haliscomenobacter. -   [4] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2] above, wherein the microbe is a transformed microbe that is     capable of expressing a protein (A) or (B):     -   (A) a protein having an amino acid sequence consisting of amino         acid residues numbers 23 to 616 of an amino acid sequence         described in SEQ ID NO: 6 of the Sequence Listing,     -   (B) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         consisting of amino acid residues 23 to 616 of the amino acid         sequence described in SEQ ID NO: 6 of the Sequence Listing, and         having activity to selectively link L-phenylalanine to an         β-ester site of the L-aspartic acid-α,β-diester through a         peptide bond. -   [5] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2], wherein the microbe is a transformed microbe that is capable of     expressing a protein (C) or (D):     -   (C) a protein having an amino acid sequence consisting of amino         acid residues numbers 21 to 619 of an amino acid sequence         described in SEQ ID NO: 12 of the Sequence Listing,     -   (D) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         consisting of amino acid residues 21 to 619 of the amino acid         sequence described in SEQ ID NO: 12 of the Sequence Listing, and         having activity to selectively link L-phenylalanine to an         α-ester site of the L-aspartic acid-α,β-diester through a         peptide bond. -   [6] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2], wherein the microbe is a transformed microbe that is capable of     expressing a protein (E) or (F) below:     -   (E) a protein having an amino acid sequence consisting of amino         acid residues numbers 23 to 625 of an amino acid sequence         described in SEQ ID NO: 18 of the Sequence Listing,     -   (F) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         consisting of amino acid residues 23 to 625 of the amino acid         sequence described in SEQ ID NO: 18 of the Sequence Listing, and         having activity to selectively link L-phenylalanine to an         α-ester site of the L-aspartic acid-α,β-diester through a         peptide bond. -   [7] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2] above, wherein the microbe is a transformed microbe that is     capable of expressing a protein (G) or (H) below:     -   (G) a protein having an amino acid sequence consisting of amino         acid residues numbers 23 to 645 of an amino acid sequence         described in SEQ ID NO: 23 of the Sequence Listing,     -   (H) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         consisting of amino acid residues 23 to 645 of the amino acid         sequence described in SEQ ID NO: 23 of the Sequence Listing, and         having activity to selectively link L-phenylalanine to an         β-ester site of the L-aspartic acid-α,β-diester through a         peptide bond. -   [8] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2], wherein the microbe is a transformed microbe that is capable of     expressing a protein (I) or (J) below:     -   (I) a protein having an amino acid sequence consisting of amino         acid residues numbers 26 to 620 of an amino acid sequence         described in SEQ ID NO: 25 of the Sequence Listing,     -   (J) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         consisting of amino acid residues 26 to 620 of the amino acid         sequence described in SEQ ID NO: 25 of the Sequence Listing, and         having activity to selectively link L-phenylalanine to an         α-ester site of the L-aspartic acid-α,β-diester through a         peptide bond. -   [9] The method for producing an α-L-aspartyl-L-phenylalanine-β-ester     (i.e., α-L-(β-o-substituted aspartyl)-L-phenylalanine) according to     [2] above, wherein the microbe is a transformed microbe that is     capable of expressing a protein (K) or (L) below:     -   (K) a protein having an amino acid sequence consisting of amino         acid residues numbers 18 to 644 of an amino acid sequence         described in SEQ ID NO: 27 of the Sequence Listing,     -   (L) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         consisting of amino acid residues 18 to 644 of the amino acid         sequence described in SEQ ID NO: 27 of the Sequence Listing, and         having activity to selectively link L-phenylalanine to an         α-ester site of the L-aspartic acid-α,β-diester through a         peptide bond. -   [10] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(β-o-substituted     aspartyl)-L-phenylalanine) according to [2], wherein the microbe is     a transformed microbe that is capable of expressing a protein (M)     or (N) below:     -   (M) a protein having an amino acid sequence described in SEQ ID         NO: 6 of the Sequence Listing,     -   (N) a protein containing a mature protein region, having an         amino acid sequence including substitution, deletion, insertion,         addition, and/or inversion of one or a plurality of amino acids         in the amino acid sequence described in SEQ ID NO: 6 of the         Sequence Listing, and having activity to selectively link         L-phenylalanine to an α-ester site of the L-aspartic         acid-α,β-diester through a peptide bond. -   [11] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(D-o-substituted     aspartyl)-L-phenylalanine) according to [2], wherein the microbe is     a transformed microbe that is capable of expressing a protein (O)     or (P) below:     -   (O) a protein having an amino acid sequence described in SEQ ID         NO: 12 of the Sequence Listing,     -   (P) a protein containing a mature protein region, having an         amino acid sequence including substitution, deletion, insertion,         addition, and/or inversion of one or a plurality of amino acids         in the amino acid sequence described in SEQ ID NO: 12 of the         Sequence Listing, and having activity to selectively link         L-phenylalanine to an α-ester site of the L-aspartic         acid-α,β-diester through a peptide bond. -   [12] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(β-o-substituted     aspartyl)-L-phenylalanine) according to claim 2, wherein the microbe     is a transformed microbe that is capable of expressing a protein (Q)     or (R) below:     -   (Q) a protein containing a mature protein region, having an         amino acid sequence described in SEQ ID NO: 18 of the Sequence         Listing,     -   (R) a protein having an amino acid sequence including         substitution, deletion, insertion, addition, and/or inversion of         one or a plurality of amino acids in the amino acid sequence         described in SEQ ID NO: 18 of the Sequence Listing, and having         activity to selectively link L-phenylalanine to an α-ester site         of the L-aspartic acid-α,β-diester through a peptide bond. -   [13] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(β-o-substituted     aspartyl)-L-phenylalanine) according to [3], wherein the microbe is     a transformed microbe that is capable of expressing a protein (S)     or (T) below:     -   (S) a protein having an amino acid sequence described in SEQ ID         NO: 23 of the Sequence Listing,     -   (T) a protein containing a mature protein region, having an         amino acid sequence including substitution, deletion, insertion,         addition, and/or inversion of one or a plurality of amino acids         in the amino acid sequence described in SEQ ID NO: 23 of the         Sequence Listing, and having activity to selectively link         L-phenylalanine to an α-ester site of the L-aspartic         acid-α,β-diester through a peptide bond. -   [14] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(β-o-substituted     aspartyl)-L-phenylalanine) according to [2], wherein the microbe is     a transformed microbe that is capable of expressing a protein (U)     or (V) below:     -   (U) a protein having an amino acid sequence described in SEQ ID         NO: 25 of the Sequence Listing,     -   (V) a protein containing a mature protein region, having an         amino acid sequence including substitution, deletion, insertion,         addition, and/or inversion of one or a plurality of amino acids         in the amino acid sequence described in SEQ ID NO: 25 of the         Sequence Listing, and having activity to selectively link         L-phenylalanine to an α-ester site of the L-aspartic         acid-α,β-diester through a peptide bond. -   [15] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(β-o-substituted     aspartyl)-L-phenylalanine) according to [2] above, wherein the     microbe is a transformed microbe that is capable of expressing a     protein (W) or (X) below:     -   (W) a protein having an amino acid sequence described in SEQ ID         NO: 27 of the Sequence Listing,     -   (X) a protein containing a mature protein region, having an         amino acid sequence including substitution, deletion, insertion,         addition, and/or inversion of one or a plurality of amino acids         in the amino acid sequence described in SEQ ID NO: 27 of the         Sequence Listing, and having activity to selectively link         L-phenylalanine to an α-ester site of the L-aspartic         acid-α,β-diester through a peptide bond. -   [16] The method for producing an     α-L-aspartyl-L-phenylalanine-β-ester (i.e., α-L-(β-o-substituted     aspartyl)-L-phenylalanine) according to [1] above, wherein the     enzyme is at least one selected from the group consisting (A) to (X)     below: -   (A) a protein having an amino acid sequence consisting of amino acid     residues numbers 23 to 616 of an amino acid sequence described in     SEQ ID NO: 6 of the Sequence Listing, -   (B) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 23 to 616 of the amino acid sequence     described in SEQ ID NO: 6 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (C) a protein having the amino acid sequence consisting of amino     acid residue numbers 21 to 619 of an amino acid sequence described     in SEQ ID NO: 12 of the Sequence Listing, -   (D) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residue numbers 21 to 619 of the amino acid sequence     described in SEQ ID NO: 12 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (E) a protein having the amino acid sequence consisting of amino     acid residues numbers 23 to 625 of an amino acid sequence described     in SEQ ID NO: 18 of the Sequence Listing, -   (F) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 23 to 625 of the amino acid sequence     described in SEQ ID NO: 18 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (G) a protein having an amino acid sequence consisting of amino acid     residues numbers 23 to 645 of an amino acid sequence described in     SEQ ID NO: 23 of the Sequence Listing, -   (H) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 23 to 645 of the amino acid sequence     described in SEQ ID NO: 23 of the Sequence Listing, and activity to     selectively linking L-phenylalanine to an α-ester site of the     L-aspartic acid-α,β-diester through a peptide bond, -   (I) a protein having an amino acid sequence consisting of amino acid     residues numbers 26 to 620 of an amino acid sequence described in     SEQ ID NO: 25 of the Sequence Listing, -   (J) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 26 to 620 of the amino acid sequence     described in SEQ ID NO: 25 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (K) a protein having an amino acid sequence consisting of amino acid     residues numbers 18 to 644 of an amino acid sequence described in     SEQ ID NO: 27 of the Sequence Listing, -   (L) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 18 to 644 of the amino acid sequence     described in SEQ ID NO: 27 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (M) a protein having an amino acid sequence described in SEQ ID NO:     6 of the Sequence Listing, -   (N) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 6 of the Sequence Listing, and     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (O) a protein having the amino acid sequence described in SEQ ID NO:     12 of the Sequence Listing, -   (P) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 12 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (Q) a protein having an amino acid sequence described in SEQ ID NO:     18 of the Sequence Listing, -   (R) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 18 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (S) a protein having an amino acid sequence described in SEQ ID NO:     23 of the Sequence Listing, -   (T) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 23 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (U) a protein having an amino acid sequence described in SEQ ID NO:     25 of the Sequence Listing, -   (V) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 25 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (W) a protein having an amino acid sequence described in SEQ ID NO:     27 of the Sequence Listing, and -   (X) a protein containing a mature protein region, having an amino     acid sequence in the amino acid sequence described in SEQ ID NO: 27     of the Sequence Listing, and having activity to selectively linking     L-phenylalanine to an α-ester site of the L-aspartic     acid-α,β-diester through a peptide bond. -   [17] The method of producing an     α-L-aspartyl-L-phenylalanine-α-methyl ester (i.e.,     α-L-aspartyl-L-phenylalanine methyl ester), comprising: a reaction     step of synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester     (also named α-L-(β-o-methyl aspartyl)-L-phenylalanine (abbreviation:     α-AMP)) by a method of producing an     α-L-aspartyl-L-phenylalanine-β-ester according to any one of claims     1 to 16; and a reaction step of converting the     α-L-aspartyl-L-phenylalanine-β-methyl ester (i.e., α-L-(β-o-methyl     aspartyl)-L-phenylalanine) to α-L-aspartyl-L-phenylalanine-α-methyl     ester

By the present invention, α-L-aspartyl-L-phenylalanine-β-ester can be easily produced. By the method of the present invention, α-L-aspartyl-L-phenylalanine-β-ester can be produced easily and at high yield with reduced use of complicated synthetic methods such as introduction/elimination of protecting groups.

Furthermore, by the present invention, α-L-aspartyl-L-phenylalanine-α-methyl ester can be produced easily, at high yield, and inexpensively.

The other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram showing amounts of enzymes that exist in a cytoplasm fraction (Cy) and a periplasm fraction (Pe).

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in the order of

<1> Method of producing α-L-aspartyl-L-phenylalanine-α-ester

-   1. Method of producing α-L-aspartyl-L-phenylalanine-β-ester -   2. Microbes used in the present invention -   3. Enzymes used in the present invention; and     <2> Method of producing α-L-aspartyl-L-phenylalanine-α-methyl ester.     <1> Method of Producing α-L-aspartyl-L-phenylalanine-β-ester -   1. Method of Producing α-L-aspartyl-L-phenylalanine-β-ester

In the method of producing α-L-aspartyl-L-phenylalanine-β-ester of the present invention (hereinafter also called “the production method of a peptide of the present invention”), L-phenylalanine and L-aspartic acid-α,β-diester are allowed to react in the presence of an enzyme having a stated peptide forming activity. That is, in the production method of a peptide of the present invention, an α-L-aspartyl-L-phenylalanine-β-ester is formed from an L-aspartic acid-α,β-diester and L-phenylalanine using an enzyme or enzyme-containing substance capable of selectively linking L-phenylalanine to the α-ester site of L-aspartic acid-α,β-diester through a peptide bond. The enzyme or enzyme-containing substance capable of selectively linking L-phenylalanine to the α-ester site of a L-aspartic acid-α,β-diester refers to an enzyme or enzyme-containing substance having an ability or activity to catalyze a reaction in which substantially, L-phenylalanine is able to perform no nucleophilic attack to a β-ester site of L-aspartic acid-α,β-diester but performs a nucleophilic attack on an α-ester site thereof only. As shown in the reference example hereinbelow, however, an enzyme or enzyme-containing substance has also been obtained that has an ability to catalyze a reaction in which substantially, L-phenylalanine is able to perform no attack on the α-ester site of an L-aspartic acid-α,β-diester but performs nucleophilic attack on the β-ester site thereof only, contrary to the above-mentioned ability, and that produces a β-L-aspartyl-L-phenylalanine-α-ester (also named β-L-(α-o-substituted aspartyl)-L-phenylalanine (abbreviation: β-ARP) from the L-aspartic acid-α,β-diester and L-phenylalanine.

The reaction formula in which L-phenylalanine performs nucleophilic attack on the α-ester site of L-aspartic acid-α,β-diester to produce an α-L-aspartyl-L-phenylalanine-β-ester (α-ARP) is shown in the following formula (I-α) (wherein “Me” represents a methyl group) by citing the case where L-aspartic acid-α,β-dimethyl ester is used as the L-aspartic acid-α,β-diester. As shown in the formula (I-α), in the peptide production method of the present invention, the amino group of L-phenylalanine reacts with the α-methyl ester site of the L-aspartic acid-α,β-dimethyl ester to form a peptide bond. On the other hand, the following formula (I-β) indicates a reaction in which the β-methyl ester site of L-aspartic acid-α,β-dimethyl ester undergoes nucleophilic attack to form β-L-aspartyl-L-phenylalanine-α-methyl ester (also named β-L-(α-o-methyl aspartyl)-L-pphenylalanine (abbreviation: β-AMP)). The peptide bond in β-AMP is formed at the β-methyl ester site of the L-aspartic acid-α,β-dimethyl ester. The enzyme or enzyme-containing substance used in the present invention accelerates substantially only a reaction as in the formula (I-α) but causes substantially no reaction as in the formula (I-β). α-APM can be produced from α-AMP through a simple reaction step (formula (II)), but α-APM cannot be produced directly from β-AMP. That is, the method of the present invention is extremely efficient as a method for producing an intermediate of α-APM and is useful for industrial production.

A method for allowing the enzyme or enzyme-containing substance to act on L-aspartic acid-α,β-diester and L-phenylalanine may be performed by mixing the enzyme or enzyme-containing substance with L-aspartic acid-α,β-diester and L-phenylalanine. More specifically, there may be used a method in which the enzyme or enzyme-containing substance is added to a solution containing an L-aspartic acid-diester and L-phenylalanine to effect reaction. When a microbe which produces the enzyme is used as the enzyme-containing substance, either the reaction may be carried out as described above, or a method which includes culturing a microbe that produces the enzyme to produce and accumulate the enzyme in the microbe or a culture liquid in which the microbe has been cultured, and adding an L-aspartic acid-α,β-diester and L-phenylalanine to the culture liquid, or the like method may be used. The thus produced α-L-aspartyl-L-phenylalanine-β-ester is recovered according to the conventional method and it can be purified, if necessary.

The “enzyme-containing substance” may be any substance so far as it contains the enzyme, and specific modes thereof include a culture of a microbe which produces the enzyme, a microbial cell separated from the culture and a treated microbial cell product of the microbe. The culture of microbe means a substance obtained by culturing a microbe, and specifically means a mixture of microbial cell, a medium used for culturing the microbe and a substance produced by the cultured microbe, and so forth. In addition, the microbial cell may be washed to use as a washed microbial cell. Moreover, the treated microbial cell product includes those obtained by subjecting the microbial cell to crushing, lysis, or freeze-drying, and further a crude enzyme recovered by treating the microbial cell and a purified enzyme obtained by further purification. As the purification-treated enzyme, a partially purified enzyme obtained by various purification methods and so forth may be used. In addition, immobilized enzymes which have been immobilized by a covalent bonding method, an adsorption method, an entrapment method, or the like may be used. Further, for some microbes to be used, a portion of the microbial cells may undergo lysis during culturing and in such a case, the supernatant of the culture liquid may be utilized as the enzyme-containing substance as well.

In addition, as the microbe that contains the enzyme, a wild strain may be used or a gene recombinant strain in which the enzyme has been expressed may be used. Such microbe is not limited to an enzyme microbial cell but the treated microbial cell products such as acetone-treated microbial cell and freeze-dried microbial cell may be used. Further, immobilized microbial cells obtained by immobilizing the treated microbial cell product using a covalent bonding method, an adsorption method, an entrapment method, or the like, or an immobilized treated microbial cell product may be used.

Use of a wild strain which is able to produce a peptide forming enzyme having an activity to form an α-L-aspartyl-L-phenylalanine-β-ester is preferred in that peptide production can be performed more readily without going through a step of making a gene recombinant strain. On the other hand, a gene recombinant strain which has been transformed so as to express a peptide forming enzyme having an activity to produce an α-L-aspartyl-L-phenylalanine-β-ester can be modified such that the peptide forming enzyme is produced in a larger amount. Thus, it is possible to synthesize an α-L-aspartyl-L-phenylalanine-β-ester in a larger amount and at a higher rate. Culturing a microbe of wild strain or gene recombinant strain in a medium to accumulate the peptide forming enzyme in the medium and/or microbe, and mixing the thus accumulated product with an L-aspartic acid-α,β-diester and L-phenylalanine can form an α-L-aspartyl-L-phenylalanine-β-ester.

Note that when cultured products, cultured microbial cells, washed microbial cells and treated microbial cell products obtained by subjecting microbial cells to crushing or lysis are used, it is often the case that an enzyme exists that decomposes the formed α-L-aspartyl-L-phenylalanine-β-ester without being involved in the formation of the α-L-aspartyl-L-phenylalanine-β-ester. In such a case, it is preferred in some occasions to add a metal protease inhibitor such as ethylenediaminetetraacetic acid (EDTA). The addition amount is in the range of 0.1 millimolar (mM) to 300 mM, preferably 1 mM to 100 mM.

The amount of enzyme or enzyme-containing substance used may be enough if it is an amount at which the target effect is demonstrated (effective amount). While a person with ordinary skill in the art can easily determine this effective amount through simple, preliminary experimentation, the use amount is, for example, about 0.01 to about 100 units (“U”) in the case of using enzyme, and about 0.1 to about 500 g/L in the case of using washed microbial cells. Note that 1 U is defined to be an amount of enzyme which allows production of 1 micromole (μmole) of L-α-aspartyl-L-phenylalanine-β-methyl ester from 100 mM L-aspartic acid-α,β-dimethyl ester and 200 mM L-phenylalanine at 25° C. in one minute.

The L-aspartic acid-α,β-diester to be used in the reaction may be any one that is condensed with L-phenylalanine to produce an α-L-aspartyl-L-phenylalanine-β ester. Examples of the L-aspartic acid-α,β-diester include L-aspartic acid-α,β-dimethyl ester and L-aspartic acid-α,β-diethyl ester. When L-aspartic acid-α,β-dimethyl ester and L-phenylalanine are allowed to react, α-L-aspartyl-L-phenylalanine-β-methyl ester (α-AMP) is produced, and when L-aspartic acid-α,β-diethyl ester and L-phenylalanine are reacted, α-L-aspartyl-L-phenylalanine-β-ethyl ester (also named α-L-(β-o-ethyl aspartyl)-L-phenylalanine (abbreviation: α-AEP)) is produced.

While the concentrations of L-aspartic acid-α,β-diester and L-phenylalanine serving as starting materials are each 1 mM to 10 mM, and preferably 0.05 M to 2 M, there may be cases in which it is preferable to add either one of the substrates in an equimolar amount or more with respect to the other substrate, and selection is made as necessary. In addition, in cases where high concentrations of substrates inhibit the reaction, these can be adjusted to concentrations that do not cause inhibition and successively added during the reaction.

The reaction temperature that allows production of α-L-aspartyl-L-phenylalanine-β-ester is 0 to 60° C., and preferably 5 to 40° C.

In addition, the reaction pH that allows production of α-L-aspartyl-L-phenylalanine-β-ester is 6.5 to 10.5, and preferably 7.0 to 10.0.

2. Microbes Used in the Present Invention

As the microbes to be used in the present invention, those microbes which have an ability to produce α-L-aspartyl-L-phenylalanine-β-ester from an L-aspartic acid-α,β-diester and L-phenylalanine may be used without particular limitation. The microbes that have an ability to produce α-L-aspartyl-L-phenylalanine-β-ester from an L-aspartic acid-α,β-diester and L-phenylalanine include, for example, microbes belonging to the genera Aeromonas, Azotobacter, Alcaligenes, Brevibacterium, Corynebacterium, Escherichia, Empedobacter, Flavobacterium, Microbacterium, Propionibacterium, Brevibacillus, Paenibacillus, Pseudomonas, Serratia, Stenotrophomonas, Sphingobacterium, Streptomyces, Xanthomonas, Williopsis, Candida, Geotrichum, Pichia, Saccharomyces, Torulaspora, Cellulophaga, Weeksella, Pedobacter, Persicobacter, Flexithrix, Chitinophaga, Cyclobacterium, Runella, Thermonema, Psychroserpens, Gelidibacter, Dyadobacter, Flammeovirga, Spirosoma, Flectobacillus, Tenacibaculum, Rhodotermus, Zobellia, Muricauda, Salegentibacter, Taxeobacter, Cytophaga, Marinilabilia, Lewinella, Saprospira, and Haliscomenobacter.

Specifically, the following may be exemplified.

Aeromonas hydrophila ATCC 13136

Azotobacter vinelandii IFO 3741

Alcaligenes faecalis FERM P-8460

Brevibacterium minutiferuna FERM BP-8277

Corynebacterium flavescens ATCC 10340

Escherichia coli FERM BP-8276

Empedobacter brevis ATCC 14234

Flavobacterium resinovorum ATCC 14231

Microbacterium arborescens ATCC 4348

Propionibacterium shermanii FERM BP-8100

Brevibacillus parabrevis ATCC 8185

Paenibacillus alvei IFO 14175

Pseudomonas fragi IFO 3458

Serratia grimesii ATCC 14460

Stenotrophomonas maltophilia ATCC 13270

Sphingobacterium sp. FERM BP-8124

Streptomyces griseolus NRRL B-1305

-   -   (Streptomyces Lavendulae)

Xanthomonas maltophilia FERM BP-5568

Williopsis saturnus IFO 0895

Candida magnoliae IFO 0705

Geotrichum fragrance CBS152.25

-   -   (Geotrichum Amycelium)

Geotrichum amycelium IFO 0905

Pichia ciferrii IFO 0905

Saccharomyces unisporus IFO 0724

Torulaspora delbrueckii IFO 0422

Cellulophaga lytica NBRC 14961

Weeksella virosa NBRC 16016

Pedobacter heparinus NBRC 12017

Persicobacter diffluens NBRC 15940

Flexithrix dorotheae NBRC 15987

Chitinophaga pinensis NBRC 15968

Cyclobacterium marinum ATCC 25205

Runella slithyformis ATCC 29530

Thermonema lapsum ATCC 43542

Psychroserpens burtonensis ATCC 700359

Gelidibacter algens ATCC 700364

Dyadobacter fermentans ATCC 700827

Flammeovirga aprica NBRC 15941

Spirosoma linguale DSMZ 74

Flectobacillus major DSMZ 103

Tenacibaculum maritimum ATCC 43398

Rhodotermus marinus DSMZ 4252

Zobellia galactanivorans DSMZ 12802

Muricauda ruestringensis DSMZ 13258

Salegentibacter salegens DSMZ 5424

Taxeobacter gelupurpurascens DSMZ 11116

Cytophaga hutchinsonii NBRC 15051

Marinilabilia salmonicolor NBRC 15948

Lewinella cohaerens ATCC 23123

Saprospira grandis ATCC 23119

Haliscomenobacter hydrossis ATCC 27775

Among the aforementioned strains of microbes, those microbes described with FERM numbers have been deposited at the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary (Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan), and can be furnished by referring to each number.

Among the aforementioned strains of microbes, those microbes described with ATCC numbers have been deposited at the American Type Culture Collection (P.O. Box 1549, Manassas, Va. 20110, the United States of America), and can be furnished by referring to each number.

Among the aforementioned strains of microbes, those microbes described with IFO numbers have been deposited at the Institute of Fermentation, Osaka (2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan), and can be furnished by referring to each number.

Among the aforementioned strains of microbes, those microbes described with NBRC numbers have been deposited at the NITE Biological Resource Center of the National Institute of Technology and Evaluation (5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan), and can be furnished by referring to each number.

Among the aforementioned strains of microbes, those microbes described with DSMZ numbers have been deposited at the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures) (Mascheroder Weg 1b, 38124 Braunschweig, Germany), and can be furnished by referring to each number.

Like the aforementioned strains, those microbes described with FERM numbers are microbes that were deposited at the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary (Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, 305-8566 Japan). Alcaligenes faecalis FERM P-8460 is a microbe that was deposited on Sep. 30, 1985 and assigned the deposit number FERM P-8460. Propionibacterium shermanii FERM P-9737 is a microbe that was originally deposited on Dec. 4, 1987 and control of this organism was subsequently transferred to international deposition under the provisions of the Budapest Treaty on Jul. 1, 2002 and was assigned the deposit number of FERM BP-8100. Xanthomonas maltophilia FERM BP-5568 is a microbe that was originally deposited on Jun. 14, 1995 and control of this organism was subsequently transferred to international deposition under the provisions of the Budapest Treaty on Jun. 14, 1996. Brevibacterium minutiferuna FERM BP-8277 was internationally deposited under the provisions of Budapest Treaty on Jan. 20, 2002. Escherichia coli FERM BP-8276 was deposited at an international depositary institution under the provisions of Budapest Treaty on Jan. 20, 2002.

Empedobacter brevis strain ATCC 14234 (strain FERM P-18545, strain FERM BP-8113) was deposited at the International Patent Organism Depositary of the independent administrative corporation, National Institute of Advanced Industrial Science and Technology (Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan) on Oct. 1, 2001 and assigned the deposit number of FERM P-18545. Control of this organism was subsequently transferred to deposition under the provisions of the Budapest Treaty at the International Patent Organism Depositary of the independent administrative corporation, National Institute of Advanced Industrial Science and Technology on Jul. 8, 2002 and was assigned the deposit number of FERM BP-8113 (indication of microbe: Empedobacter brevis strain AJ 13933).

Sphingobacterium sp. strain AJ 110003 was deposited at the International Patent Organism Depositary of the independent administrative corporation, National Institute of Advanced Industrial Science and Technology (Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan) on Jul. 22, 2002, and was assigned the deposit number of FERM BP-8124.

Note that the strain AJ 110003 (FERM BP-8124) was identified to be the aforementioned Sphingobacterium sp. by the identification experiment described below. The strain FERM BP-8124 is a Gram-negative rod (0.7 to 0.8×1.5 to 2.0 μm) that forms no spore and is not motile. Its colonies are round with a completely smooth border, contain low protrusions and have a glossy, light yellow color. The organism grows at 30° C. and is catalase positive, oxidase positive and negative for the OF test (glucose), and was identified as a bacterium belonging to the genus Sphingobacterium based on these properties. Moreover, because of the properties that it is negative for nitrate reduction, negative for indole production, negative for acid production from glucose, arginine dihydrolase negative, urease positive, esculin hydrolysis positive, gelatin hydrolysis negative, β-galactosidase positive, glucose assimilation positive, L-arabinose assimilation negative, D-mannose assimilation positive, D-mannitol assimilation negative, N-acetyl-D-glucosamine assimilation positive, maltose assimilation positive, potassium gluconate assimilation negative, n-capric acid assimilation negative, adipic acid assimilation negative, dl-malic acid assimilation negative, sodium citrate assimilation negative, phenyl acetate assimilation negative and cytochrome oxidase positive, it was determined to have properties that are similar to those of Sphingobacterium multivorum or Sphingobacterium spiritivorum. Moreover, although results of analyzing analyses on the homology of the base sequence of the 16S rRNA gene indicate the highest degree of homology was exhibited with Sphingobacterium multivorum (98.8%), there were was no strain with which the bacterial strain matched completely. Accordingly, this bacterial strain was therefore identified as Sphingobacterium sp.

As these microbes, either wild strains or mutant strains can be used or recombinant strains induced by cell fusion or genetic techniques such as genetic manipulation can be used.

To obtain microbial cells of such microbes, the microbes can be cultured and grown in a suitable medium. There is no particular restriction on the medium used for this purpose so far as it allows the microbes to grow. This medium may be an ordinary medium containing ordinary carbon sources, nitrogen sources, phosphorus sources, sulfur sources, inorganic ions, and organic nutrient sources as necessary.

For example, any carbon source may be used so far as the microbes can utilize it. Specific examples of the carbon source that can be used include sugars such as glucose, fructose, maltose and amylose, alcohols such as sorbitol, ethanol and glycerol, organic acids such as fumaric acid, citric acid, acetic acid and propionic acid and their salts, hydrocarbons such as paraffin as well as mixtures thereof.

Examples of nitrogen sources that can be used include ammonium salts of inorganic acids such as ammonium sulfate and ammonium chloride, ammonium salts of organic acids such as ammonium fumarate and ammonium citrate, nitrates such as sodium nitrate and potassium nitrate, organic nitrogen compounds such as peptones, yeast extract, meat extract and corn steep liquor as well as mixtures thereof.

In addition, nutrient sources used in ordinary media, such as inorganic salts, trace metal salts and vitamins, can also be suitably mixed and used.

There is no particular restriction on culturing conditions, and culturing can be carried out, for example, for about 12 to about 48 hours while properly controlling the pH and temperature within a pH range of 5 to 8 and a temperature range of 15 to 40° C., respectively, under aerobic conditions.

3. Enzymes Used in the Present Invention

In the method for producing peptide according to the present invention described above, an enzyme which has an ability to selectively link L-phenylalanine to the α-ester site of an L-aspartic acid-α,β-diester through a peptide bond is used. In the method for producing peptide according to the present invention, the enzyme is not limited by its origination and procuring method so far as it has such an activity. Hereinafter, purification of enzymes used in the present invention and utilization of techniques of genetic engineering will be explained.

(3-1) Microbes Having an Enzyme which can be Used for the Production Method of the Present Invention

As microbes which produce an enzyme of the present invention, all the microbes that have an ability to produce an α-L-aspartyl-L-phenylalanine-β-ester from an L-aspartic acid-α,β-diester and L-phenylalanine can be used. The microbes include bacteria and the like that belong to genera selected from the group consisting of Aeromonas, Azotobacter, Alcaligenes, Brevibacterium, Corynebacterium, Escherichia, Empedobacter, Flavobacterium, Microbacterium, Propionibacterium, Brevibacillus, Paenibacillus, Pseudomonas, Serratia, Stenotrophomonas, Sphingobacterium, Streptomyces, Xanthomonas, Williopsis, Candida, Geotrichum, Pichia, Saccharomyces, Torulaspora, Cellulophaga, Weeksella, Pedobacter, Persicobacter, Flexithrix, Chitinophaga, Cyclobacterium, Runella, Thermonema, Psychroserpens, Gelidibacter, Dyadobacter, Flammeovirga, Spirosoma, Flectobacillus, Tenacibaculum, Rhodotermus, Zobellia, Muricauda, Salegentibacter, Taxeobacter, Cytophaga, Marinilabilia, Lewinella, Saprospira, and Haliscomenobacter. More specifically, the microbes include Empedobacter brevis ATCC 14234 (FERM P-18545 strain, FERM BP-8113 strain (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002)), Sphingobacterium sp. FERM BP-8124 strain (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit date: Jul. 22, 2002), Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan), Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany), Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), and Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) and so forth. Empedobacter brevis ATCC 14234 strain (FERM P-18545 strain, FERM BP-8113 strain (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002)) and Sphingobacterium sp. FERM BP-8124 strain (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit date: Jul. 22, 2002), Pedobacter heparinus IFO 12017 strain (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan), Taxeobacter gelupurpurascens DSMZ 11116 strain (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1 b, 38124 Braunschweig, Germany), Cyclobacterium marinum ATCC 25205 strain (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), and Psycloserpens burtonensis ATCC 700359 strain (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) and the like are microbes selected by the present inventors as a result of search of enzyme producing microbes which produce an α-L-aspartyl-L-phenylalanine-β-ester from an L-aspartic acid-α,β-diester and L-phenylalanine at high yield.

(3-2) Purification of Enzyme

As was previously mentioned, the peptide-forming enzyme used in the present invention can be purified from bacteria belonging to, for example, the genus Empedobacter. A method for isolating and purifying a peptide-forming enzyme from Empedobacter brevis is explained as an example of purification of the enzyme.

First, a microbial cell extract is prepared from microbial cells of Empedobacter brevis, for example, the strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) by disrupting the cells using a physical method such as ultrasonic crushing or an enzymatic method using a cell wall-dissolving enzyme and removing the insoluble fraction by centrifugal separation and so forth. The peptide-producing enzyme can then be purified by fractionating the cell extract obtained in the above manner by combining ordinary protein purification methods such as anion exchange chromatography, cation exchange chromatography or gel filtration chromatography.

An example of a carrier for use in anion exchange chromatography is Q-Sepharose HP (manufactured by Amersham). The enzyme is recovered in the non-adsorbed fraction under conditions of pH 8.5 when the cell extract containing the enzyme is allowed to pass through a column packed with the carrier.

An example of a carrier for use in cation exchange chromatography is MonoS HR (manufactured by Amersham). After adsorbing the enzyme onto the column by allowing the cell extract containing the enzyme to pass through a column packed with the carrier and then washing the column, the enzyme is eluted with a buffer solution having a high salt concentration. At that time, the salt concentration may be sequentially increased or a concentration gradient may be applied. For example, in the case of using MonoS HR, the enzyme adsorbed onto the column is eluted at an NaCl concentration of about 0.2 to about 0.5 M.

The enzyme purified in the manner described above can then be further uniformly purified by gel filtration chromatography and so forth. An example of the carrier for use in gel filtration chromatography is Sephadex 200 pg (manufactured by Amersham).

In the aforementioned purification procedure, the fraction containing the enzyme can be verified by assaying the peptide-forming activity of each fraction according to the method indicated in the examples to be described later. The internal amino acid sequence of the enzyme purified in the manner described above is shown in SEQ ID NO: 1 and SEQ ID NO: 2 of the Sequence Listing.

(3-3) Isolation DNA, Production of Transformant and Purification of Peptide-Forming Enzyme

(3-3-1) Isolation of DNA

The inventors of the present invention first succeeded in isolating one type of DNA of a peptide-forming enzyme that can be used in the peptide production method of the present invention from Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002).

A DNA having a base sequence consisting of bases numbers 61 to 1908 of the base sequence described in SEQ ID NO: 5, which is a DNA of the present invention, was isolated from Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002). The DNA having the base sequence consisting of bases numbers 61 to 1908 is a code sequence (CDS) portion. In the base sequence consisting of bases numbers 61 to 1908 is contained a signal sequence region and a mature protein region. The signal sequence region is a region that consists of bases numbers 61 to 126, while the mature protein region is a region that consists of bases numbers 127 to 1908. Namely, the present invention provides both a gene for a peptide-forming enzyme protein that contains a signal sequence, and a gene for a peptide-forming enzyme protein in the form of a mature protein. The signal sequence contained in the sequence described in SEQ ID NO: 5 is a kind of leader sequence. The main function of a leader peptide encoded by the leader sequence is presumed to be excretion from inside the cell membrane to outside the cell membrane. The protein encoded by bases numbers 127 to 1908, namely the-ester site excluding the leader peptide, is presumed to be a mature protein and exhibit a high degree of peptide-forming activity.

The DNA consisting of the base sequence that consists of bases numbers 61 to 1917 described in SEQ ID NO: 11, which is also a DNA of the present invention, was isolated from Sphingobacterium sp. strain FERM BP-8124 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, lbaraki-ken, Japan, International deposit date: Jul. 22, 2002). The DNA consisting of the base sequence that consists of bases numbers 61 to 1917 is a code sequence (CDS) portion. In the base sequence consisting of bases numbers 61 to 1917, a signal sequence region and a mature protein region are contained. The signal sequence region is a region that consists of bases numbers 61 to 120, while the mature protein region is a region that consists of bases numbers 121 to 1917. Namely, the present invention provides both a gene for a peptide-forming enzyme protein that contains a signal sequence, and a gene for a peptide-forming enzyme protein in the form of a mature protein. The signal sequence contained in the sequence described in SEQ ID NO: 11 is a kind of leader sequence. The main function of a leader peptide encoded by the leader sequence is presumed to be excretion from inside the cell membrane to outside the cell membrane. The protein encoded by bases numbers 121 to 1917, namely the portion excluding the leader peptide, is presumed to be a mature protein and exhibit a high degree of peptide-forming activity.

The DNA consisting of the base sequence that consists of bases numbers 61 to 1935 described in SEQ ID NO: 17, which is also a DNA of the present invention, was isolated from Pedobacter heparinus strain IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan). The DNA consisting of the base sequence that consists of bases numbers 61 to 1935 described in SEQ ID NO:17 is a code sequence (CDS) portion. In the base sequence consisting of bases numbers 61 to 1935, a signal sequence region and a mature protein region are contained. The signal sequence region is a region that consists of bases numbers 61 to 126, while the mature protein region is a region that consists of bases numbers 127 to 1935. Namely, the present invention provides both a gene for a peptide-forming enzyme protein that contains a signal sequence, and a gene for a peptide-forming enzyme protein in the form of a mature protein. The signal sequence contained in the sequence described in SEQ ID NO: 17 is a kind of leader sequence. The main function of a leader peptide encoded by the leader sequence is presumed to be excretion from inside the cell membrane to outside the cell membrane. The protein encoded by bases numbers 127 to 1935, namely the portion excluding the leader peptide, is presumed to be a mature protein and exhibit a high degree of peptide-forming activity.

The DNA consisting of the base sequence that consists of bases numbers 61 to 1995 described in SEQ ID NO: 22, which is also a DNA of the present invention, was isolated from Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). The DNA consisting of the base sequence that consists of bases numbers 61 to 1995 described in SEQ ID NO:22 is a code sequence (CDS) portion. In the base sequence consisting of bases numbers 61 to 1995, a signal sequence region and a mature protein region are contained. The signal sequence region is a region that consists of bases numbers 61 to 126, while the mature protein region is a region that consists of bases numbers 127 to 1995. Namely, the present invention provides both a gene for a peptide-forming enzyme protein that contains a signal sequence, and a gene for a peptide-forming enzyme protein in the form of a mature protein. The signal sequence contained in the sequence described in SEQ ID NO: 22 is a kind of leader sequence. The main function of a leader peptide encoded by the leader sequence is presumed to be excretion from inside the cell membrane to outside the cell membrane. The protein encoded by bases numbers 127 to 1995, namely the portion excluding the leader peptide, is presumed to be a mature protein and exhibit a high degree of peptide-forming activity.

The DNA consisting of the base sequence that consists of bases numbers 29 to 1888 described in SEQ ID NO: 24, which is also a DNA of the present invention, was isolated from Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). The DNA consisting of the base sequence that consists of bases numbers 29 to 1888 described in SEQ ID NO:24 is a code sequence (CDS) portion. In the base sequence consisting of bases numbers 29 to 1888, a signal sequence region and a mature protein region are contained. The signal sequence region is a region that consists of bases numbers 29 to 103, while the mature protein region is a region that consists of bases numbers 104 to 1888. Namely, the present invention provides both a gene for a peptide-forming enzyme protein that contains a signal sequence, and a gene for a peptide-forming enzyme protein in the form of a mature protein. The signal sequence contained in the sequence described in SEQ ID NO: 24 is a kind of leader sequence. The main function of a leader peptide encoded by the leader sequence is presumed to be excretion from inside the cell membrane to outside the cell membrane. The protein encoded by bases numbers 104 to 1888, namely the portion excluding the leader peptide, is presumed to be a mature protein and exhibit a high degree of peptide-forming activity.

The DNA consisting of the base sequence that consists of bases numbers 61 to 1992 described in SEQ ID NO: 26, which is also a DNA of the present invention, was isolated from Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). The DNA consisting of the base sequence that consists of bases numbers 61 to 1992 described in SEQ ID NO:26 is a code sequence (CDS) portion. In the base sequence consisting of bases numbers 61 to 1992, a signal sequence region and a mature protein region are contained. The signal sequence region is a region that consists of bases numbers 61 to 111, while the mature protein region is a region that consists of bases numbers 112 to 1992. Namely, the present invention provides both a gene for a peptide-forming enzyme protein that contains a signal sequence, and a gene for a peptide-forming enzyme protein in the form of a mature protein. The signal sequence contained in the sequence described in SEQ ID NO: 26 is a kind of leader sequence. The main function of a leader peptide encoded by the leader sequence is presumed to be excretion from inside the cell membrane to outside the cell membrane. The protein encoded by bases numbers 112 to 1992, namely the portion excluding the leader peptide, is presumed to be a mature protein and exhibit a high degree of peptide-forming activity.

Furthermore, the various gene recombination techniques indicated below can be carried out in accordance with the descriptions in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989) and other publications.

A DNA encoding an enzyme that can be used in the present invention can be acquired by polymerase chain reaction (PCR, refer to White, T. J. et al., Trends Genet., 5, 185 (1989)) or hybridization from a chromosomal DNA or a DNA library of Empedobacter brevis, Sphingobacterium sp., Pedobacter heparinus, Taxeobacter gelupurpurascens, Cyclobacterium marinum, or Psychroserpens burtonensis. Primers used in PCR can be designed based on the internal amino acid base sequences determined on the basis of purified peptide-forming enzyme as explained in the previous section (3). In addition, since the base sequences of the peptide-forming enzyme genes (SEQ ID NO: 5, SEQ ID NO: 11, SEQ ID NO:17, SEQ ID NO:22, SEQ ID NO:24, and SEQ ID NO:26) have been identified by the present invention, primers or hybridization probes can be designed on the basis of these base sequences, and the gene can be isolated using the probes. If primers having sequences corresponding to the 5′-nontranslated region and 3′-nontranslated region, respectively, are used as PCR primers, the full-length encoded region of the enzyme can be amplified. Taking as an example the case of amplifying a region containing both the leader sequence and a mature protein encoding region as described in SEQ ID NO: 5, specific examples of primers include a primer having a base sequence of the region upstream of base number 61 in SEQ ID NO: 5 for the 5′-side primer, and a primer having a sequence complementary to the base sequence of the region downstream of base number 1908 for the 3′-side primer.

Primers can be synthesized, for example, according to ordinary methods using the phosphoamidite method (refer to Tetrahedron Letters (1981), 22, 1859) by use of the Model 380B DNA Synthesizer manufactured by Applied Biosystems. The PCR reaction can be carried out, for example, by using the Gene Amp PCR System 9600 (Perkin-Elmer) and the Takara LA PCR In Vitro Cloning Kit (Takara Shuzo) in accordance with the method specified by the supplier such as the manufacturer.

A DNA that encodes an enzyme that can be used in the peptide production method of the present invention, regardless of whether the DNA contains a leader sequence or not, includes a DNA that is substantially identical to the DNA consisting of the CDS described in SEQ ID NO: 5 of the Sequence Listing. Namely, a DNA substantially identical to the DNA of the present invention can be obtained by isolating a DNA that hybridizes a DNA consisting of a base sequence complementary to the CDS described in SEQ ID NO: 5 of the Sequence Listing or with a probe prepared from the base sequence under stringent conditions and encodes a protein having peptide-forming activity from a DNA encoding the mutant enzyme or cells that possess that DNA.

The DNA of the present invention, regardless of whether it contains a leader sequence or not, includes a DNA that is substantially identical to the DNA consisting of the CDS described in SEQ ID NO: 11 of the Sequence Listing. Namely, a DNA substantially identical to the DNA of the present invention can be obtained by isolating a DNA that hybridizes a DNA consisting of a base sequence complementary to the CDS described in SEQ ID NO: 11 of the Sequence Listing or with a probe prepared from the base sequence under stringent conditions and encodes a protein having peptide-forming activity from a DNA encoding the mutant enzyme or cells that possess that DNA.

The DNA of the present invention, regardless of whether it contains a leader sequence or not, includes a DNA that is substantially identical to the DNA consisting of the CDS described in SEQ ID NO: 17 of the Sequence Listing. Namely, a DNA substantially identical to the DNA of the present invention can be obtained by isolating a DNA that hybridizes with a DNA consisting of a base sequence complementary to the CDS described in SEQ ID NO: 17 of the Sequence Listing or with a probe prepared from the base sequence under stringent conditions and encodes a protein having peptide-forming activity from a DNA encoding the mutant enzyme or cells that possess that DNA.

The DNA of the present invention, regardless of whether it contains a leader sequence or not, includes a DNA that is substantially identical to the DNA consisting of the CDS described in SEQ ID NO: 22 of the Sequence Listing. Namely, a DNA substantially identical to the DNA of the present invention can be obtained by isolating a DNA that hybridizes with a DNA consisting of a base sequence complementary to the CDS described in SEQ ID NO: 22 of the Sequence Listing or with a probe prepared from the base sequence under stringent conditions and encodes a protein having peptide-forming activity from a DNA encoding the mutant enzyme or cells that possess that DNA.

The DNA of the present invention, regardless of whether it contains a leader sequence or not, includes a DNA that is substantially identical to the DNA consisting of the CDS described in SEQ ID NO: 24 of the Sequence Listing. Namely, a DNA substantially identical to the DNA of the present invention can be obtained by isolating a DNA that hybridizes with a DNA consisting of a base sequence complementary to the CDS described in SEQ ID NO: 24 of the Sequence Listing or with a probe prepared from the base sequence under stringent conditions and encodes a protein having peptide-forming activity from a DNA encoding the mutant enzyme or cells that possess that DNA.

The DNA of the present invention, regardless of whether it contains a leader sequence or not, includes a DNA that is substantially identical to the DNA consisting of the CDS described in SEQ ID NO: 26 of the Sequence Listing. Namely, a DNA substantially identical to the DNA of the present invention can be obtained by isolating a DNA that hybridizes with a DNA consisting of a base sequence complementary to the CDS described in SEQ ID NO: 26 of the Sequence Listing or with a probe prepared from the base sequence under stringent conditions and encodes a protein having peptide-forming activity from a DNA encoding the mutant enzyme or cells that possess that DNA.

A probe can be produced, for example, in accordance with established methods based on, for example, the base sequence described in SEQ ID NO: 5 of the Sequence Listing. In addition, a method for isolating a target DNA by using a probe to find a DNA that hybridizes with the probe may also be carried out in accordance with established methods. For example, a DNA probe can be produced by amplifying a base sequence cloned in a plasmid or phage vector, cleaving the base sequence desired to be used as a probe with a restriction enzyme and then extracting the desired base sequence. The portion to be cleaved out can be adjusted depending on the target DNA.

The term “under a stringent condition” as used herein refers to a condition under which a so-called specific hybrid is formed but no non-specific hybrid is formed. It is difficult to precisely express this condition in numerical values. For example, mention may be made of a condition under which DNAs having high homologies, for example, 50% or more, preferably 80% or more, more preferably 90% or more, hybridize with each other and DNAs having lower homologies than these do not hybridize with each other, or ordinary conditions for rinse in Southern hybridization under which hybridization is performed at 60° C. in a salt concentration corresponding 1×SSC and 0.1% SDS, preferably 0.1×SSC and 0.1% SDS. Although the genes that hybridize under such conditions include those genes in which stop codons have occurred at certain locations along their sequences or which have lost activity due to a mutation in the active center, these can be easily removed by ligating them to a commercially available expression vector, expressing them in a suitable host, and assaying the enzyme activity of the expression product using a method to be described later.

However, in the case of a base sequence that hybridizes under stringent conditions as described above, it is preferable that the protein encoded by that base sequence retains about a half or more, preferably 80% or more, and more preferably 90% or more, of the enzyme activity of the protein having the amino acid sequence encoded by the original base sequence serving as the base be retained under conditions of 50° C. and pH 8. For example, when explained for on the case of, for example, a base sequence that hybridizes under stringent conditions with a DNA that has a base sequence complementary to the base sequence consisting of bases numbers 127 to 1908 of the base sequence described in SEQ ID NO: 5, it is preferable that the protein encoded by that base sequence retains about a half or more, preferably 80% or more, and more preferably 90% or more, of the enzyme activity of the protein having an amino acid sequence that consists of amino acid residues numbers 23 to 616 of the amino acid sequence described in SEQ ID NO: 6 under conditions of 50° C. and pH 8.

An amino acid sequence encoded by the CDS described in SEQ ID NO: 5 of the Sequence Listing is shown in SEQ ID NO: 6 of the Sequence Listing. An amino acid sequence encoded by the CDS described in SEQ ID NO: 11 of the Sequence Listing is shown in SEQ ID NO: 12 of the Sequence Listing. An amino acid sequence encoded by the CDS described in SEQ ID NO.: 17 of the Sequence Listing is shown in SEQ ID NO: 18 of the Sequence Listing. An amino acid sequence encoded by the CDS described in SEQ ID NO: 22 of the Sequence Listing is shown in SEQ ID NO: 23 of the Sequence Listing. An amino acid sequence encoded by the CDS described in SEQ ID NO: 24 of the Sequence Listing is shown in SEQ ID NO: 25 of the Sequence Listing. An amino acid sequence encoded by the CDS described in SEQ ID NO: 26 of the Sequence Listing is shown in SEQ ID NO: 27 of the Sequence Listing.

The entire amino acid sequence described in SEQ ID NO: 6 contains a leader peptide and a mature protein region, with amino acid residues numbers 1 to 22 constituting the leader peptide, and amino acid residues numbers 23 to 616 constituting the mature protein region.

The entire amino acid sequence described in SEQ ID NO: 11 includes a leader peptide and a mature protein region, with amino acid residues numbers 1 to 20 constituting the leader peptide, and amino acid residues numbers 21 to 619 constituting the mature protein region.

The entire amino acid sequence described in SEQ ID NO: 18 contains a leader peptide and a mature protein region, with amino acid residues numbers 1 to 22 constituting the leader peptide, and amino acid residues numbers 23 to 625 constituting the mature protein region.

The entire amino acid sequence described in SEQ ID NO: 23 contains a leader peptide and a mature protein region, with amino acid residues numbers 1 to 22 constituting the leader peptide, and amino acid residues numbers 23 to 645 constituting the mature protein region.

The entire amino acid sequence described in SEQ ID NO: 25 contains a leader peptide and a mature protein region, with amino acid residues numbers 1 to 25 constituting the leader peptide, and amino acid residues numbers 26 to 620 constituting the mature protein region.

The entire amino acid sequence described in SEQ ID NO: 27 contains a leader peptide and a mature protein region, with amino acid residues numbers 1 to 17 constituting the leader peptide, and amino acid residues numbers 18 to 644 constituting the mature protein region.

The protein encoded by the DNA of the present invention is a protein in which the mature protein has peptide-forming activity, and a DNA that encodes a protein substantially identical to a protein having the amino acid sequence described in SEQ ID NO: 6, SEQ ID NO: 12, SEQ ID NO: 18, SEQ ID NO: 23, SEQ ID NO: 25, or SEQ ID NO: 27 of the Sequence Listing, regardless of whether it contains a leader peptide or not, is also included in the DNA of the present invention. (Note that, base sequences are specified from amino acid sequences in accordance with the codes of the universal codons.) Namely, the present invention provides DNAs that encode proteins indicated in (A) to (X) below:

-   (A) a protein having an amino acid sequence consisting of amino acid     residues numbers 23 to 616 of an amino acid sequence described in     SEQ ID NO: 6 of the Sequence Listing, -   (B) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 23 to 616 of the amino acid sequence     described in SEQ ID NO: 6 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (C) a protein having the amino acid sequence consisting of amino     acid residue numbers 21 to 619 of an amino acid sequence described     in SEQ ID NO: 12 of the Sequence Listing, -   (D) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residue numbers 21 to 619 of the amino acid sequence     described in SEQ ID NO: 12 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (E) a protein having the amino acid sequence consisting of amino     acid residues numbers 23 to 625 of an amino acid sequence described     in SEQ ID NO: 18 of the Sequence Listing, -   (F) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 23 to 625 of the amino acid sequence     described in SEQ ID NO: 18 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (G) a protein having an amino acid sequence consisting of amino acid     residues numbers 23 to 645 of an amino acid sequence described in     SEQ ID NO: 23 of the Sequence Listing, -   (H) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 23 to 645 of the amino acid sequence     described in SEQ ID NO: 23 of the Sequence Listing, and activity to     selectively linking L-phenylalanine to an α-ester site of the     L-aspartic acid-α,β-diester through a peptide bond, -   (I) a protein having an amino acid sequence consisting of amino acid     residues numbers 26 to 620 of an amino acid sequence described in     SEQ ID NO: 25 of the Sequence Listing, -   (J) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 26 to 620 of the amino acid sequence     described in SEQ ID NO: 25 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (K) a protein having an amino acid sequence consisting of amino acid     residues numbers 18 to 644 of an amino acid sequence described in     SEQ ID NO: 27 of the Sequence Listing, -   (L) a protein having an amino acid sequence including substitution,     deletion, insertion, addition, and/or inversion of one or a     plurality of amino acids in the amino acid sequence consisting of     amino acid residues numbers 18 to 644 of the amino acid sequence     described in SEQ ID NO: 27 of the Sequence Listing, and having     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (M) a protein having an amino acid sequence described in SEQ ID NO:     6 of the Sequence Listing, -   (N) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 6 of the Sequence Listing, and     activity to selectively linking L-phenylalanine to an α-ester site     of the L-aspartic acid-α,β-diester through a peptide bond, -   (O) a protein having the amino acid sequence described in SEQ ID NO:     12 of the Sequence Listing, -   (P) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 12 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (Q) a protein having an amino acid sequence described in SEQ ID NO:     18 of the Sequence Listing, -   (R) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 18 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (S) a protein having an amino acid sequence described in SEQ ID NO:     23 of the Sequence Listing, -   (T) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 23 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (U) a protein having an amino acid sequence described in SEQ ID NO:     25 of the Sequence Listing, -   (V) a protein containing a mature protein region, having an amino     acid sequence including substitution, deletion, insertion, addition,     and/or inversion of one or a plurality of amino acids in the amino     acid sequence described in SEQ ID NO: 25 of the Sequence Listing,     and activity to selectively linking L-phenylalanine to an α-ester     site of the L-aspartic acid-α,β-diester through a peptide bond, -   (W) a protein having an amino acid sequence described in SEQ ID NO:     27 of the Sequence Listing, and -   (X) a protein containing a mature protein region, having an amino     acid sequence in the amino acid sequence described in SEQ ID NO: 27     of the Sequence Listing, and having activity to selectively linking     L-phenylalanine to an α-ester site of the L-aspartic     acid-α,β-diester through a peptide bond.

Here, although the meaning of the term “a plurality of” varies depending on the locations and types of the amino acid residues in the three-dimensional structure of the protein, it is within a range that does not significantly impair the three-dimensional structure and activity of the protein of the amino acid residues, and is specifically 2 to 50, preferably 2 to 30, and more preferably 2 to 10. However, in the case of amino acid sequences including substitution, deletion, insertion, addition, and/or inversion of one or a plurality of amino acids in amino acid sequences of the proteins of (B), (D), (F), (H), (J), (L), (N), (P), (R), (T), (V) or (X), it is preferable that the proteins retain about half or more, more preferably 80% or more, and even more preferably 90% or more of the enzyme activity of the proteins in the state where no mutation is included, under conditions of 50° C. and pH 8. For example, explanation will be made in the case of (B); in the case of the amino acid sequence (B) including substitution, deletion, insertion, addition, and/or inversion of one or a plurality of amino acids in an amino acid sequence described in SEQ ID NO: 6 of the Sequence Listing, it is preferable that this protein retains about half or more, more preferably 80% or more, and even more preferably 90% or more of the enzyme activity of the protein having the amino acid sequence described in SEQ ID NO: 6 of the Sequence Listing, under conditions of 50° C. and pH 8.

A mutation of an amino acid like that indicated in the aforementioned (B) and so forth is obtained by modifying the base sequence so that an amino acid of a specific-ester site in the present enzyme gene is substituted, deleted, inserted or added by, for example, -ester site-directed mutagenesis. In addition, a modified DNA like that described above can also be acquired by mutagenesis treatment known in the art. Mutagenesis treatment refers to, for example, a method in which a DNA encoding the present enzyme is treated in vitro with hydroxylamine and so forth, as well as a method in which Escherichia bacteria that possess a DNA encoding the present enzyme are treated by a mutagen normally used in artificial mutagenesis, such as ultraviolet irradiation, N-methyl-N′-nitro-N-nitrosoguanidine (NTG) or nitrous acid.

In addition, naturally-occurring mutations such as differences attributable to a microbe species or strain are also included in the base substitution, deletion, insertion, addition and/or inversion described above. By expressing a DNA having such a mutation in suitable cells and investigating the enzyme activity of the expression product, a DNA can be obtained that encodes a protein substantially identical to the protein described in SEQ ID NO: 6, 12, 18, 23, 25 or 27 of the Sequence Listing.

(3-3-2) Preparation of Transformants and Production of Peptide-Forming Enzymes

Peptide-forming enzymes that can be used in the method of producing a peptide according to the present invention can be produced by introducing the DNA explained in (3-3-1) above into a suitable host and expressing the DNA in that host.

With respect to hosts for expressing a protein specified by the DNA, examples of the hosts that can be used include various prokaryotic cells including Escherichia bacteria such as Escherichia coli, Empedobacter bacteria, Sphingobacterium bacteria, Flavobacterium bacteria and Bacillus subtilis, as well as various eukaryotic cells including Saccharomyces cerevisiae, Pichia stipitis and Aspergillus oryzae.

A recombinant DNA used to introduce a DNA into a host can be prepared by inserting the DNA to be introduced into a vector corresponding to the type of host in which the DNA is to be expressed, in such a form that the protein encoded by that DNA can be expressed. In the case where a promoter unique to a peptide-forming enzyme gene of Empedobacter brevis and so forth functions in the host cells, the promoter can be used as a promoter for expressing the DNA of the present invention. In addition, another promoter that acts in the host cells may be ligated to the DNA of the present invention, and the DNA may be expressed under the control of the promoter as necessary.

Examples of transformation methods for introducing a recombinant DNA into host cells include the method of D. M. Morrison (see Methods in Enzymology, 68, 326 (1979)) or the method in which DNA permeability is increased by treating receptor microbial cells with calcium chloride (see Mandel, H. and Higa, A., J. Mol. Biol., 53, 159 (1970)).

In the case of mass production of a protein using recombinant DNA technology, conjugating the protein within a transformant that produces the protein to form an inclusion body of protein is also a preferable mode for carrying out the present invention. Advantages of this expression and production method include protection of the target protein from digestion by proteases present within the microbial cells, and simple and easy purification of the target protein by disrupting the microbial cells followed by centrifugal separation and so forth.

The inclusion body of protein obtained in this manner is solubilized with a protein denaturant and the protein is converted to a properly folded, physiologically active protein through an activity regeneration procedure that consists primarily of removal of the denaturant. There are numerous examples of this, including regeneration of the activity of human interleukin-2 (see Japanese Patent Application Laid-open Publication No. S61-257931).

To obtain an active protein from inclusion bodies of, a series of procedures including solubilization and activity regeneration are required, and the procedure is more complex than in the case of producing the active protein directly. However, in the case of producing a protein that has a detrimental effect on microbial growth in large volumes within microbial cells, that effect can be suppressed by accumulating the proteins in the form of inclusion bodies of inactive protein within the microbial cells.

Examples of mass production methods for producing a target protein in the form of inclusion bodies include a method in which a target protein is expressed independently under the control of a powerful promoter, and a method in which a target protein is expressed in the form of a fused protein with a protein that is known to be expressed in a large volume.

Hereinafter, the present invention will be explained more specifically taking as an example a method for producing transformed Escherichia coli and using that transformed microbe to produce a peptide-forming enzyme. Furthermore, in the case of producing peptide-forming enzyme in a microbe such as Escherichia coli, a DNA that encodes a precursor protein containing a leader sequence may be incorporated or a DNA that consists only of a mature protein region that does not contain a leader sequence may be incorporated, and the DNA can be suitably selected for the protein encoding sequence depending on the production conditions, form, usage conditions and so forth of the enzyme to be produced.

Promoters normally used in the production of heterogeneous proteins in Escherichia. coli can be used as a promoter for expressing a DNA encoding a peptide-forming enzyme. Examples of such promoters include T7 promoter, lac promoter, trp promoter, trc promoter, tac promoter, lambda phage PR promoter, PL promoter and other powerful promoters. In addition, examples of vectors that can be used include pUC19, pUC18, pBR322, pHSG299, pHSG298, pHSG399, pHSG398, RSF1010, pMW119, pMW118, pMW219, and pMW218. Besides, vectors of phage DNA can also be used. Moreover, expression vectors that contain promoters and are capable of expressing an inserted DNA sequence can be used.

To produce peptide-forming enzyme in the form of a fused protein inclusion body, a gene that encodes another protein, and preferably a hydrophilic peptide, is ligated upstream or downstream of the peptide-forming enzyme gene to obtain a fused protein gene. The gene that encodes another protein in this manner may be any gene that increases the amount of the fused protein accumulated and enhances the solubility of the fused protein after the denaturation and regeneration steps. Examples of candidates for such genes include T7 gene 10, β-galactosidase gene, dehydrofolate reductase gene, γ-interferon gene, interleukin-2 gene and prochymosin gene.

When these genes are ligated to the genes that encode peptide-forming enzymes, the genes are ligated so that reading frames of codons are consistent. It is recommended that the genes be ligated at a proper restriction enzyme-ester site or a synthetic DNA having a proper sequence be utilized.

Further, to increase a production amount of the peptide-forming enzyme, it is preferable in some cases that a terminator, which is a transcription terminating sequence, be ligated to downstream of the fusion protein gene. The terminator includes, for example, a T7 terminator, an fd phage terminator, a T4 terminator, a tetracycline resistant gene terminator, and an Escherichia coli trpA gene terminator.

As the vectors for introducing a gene that encodes a peptide-forming enzyme or a fused protein between the peptide-forming enzyme and another protein in Escherichia coli are preferred so-called multi-copy type vectors, examples of which include a plasmid having a replicator derived from ColE1, for example, a pUC-based plasmid, and a pBR322-based plasmid or derivatives thereof. The “derivatives” as used herein refer to those plasmids that are subjected modification by substitution, deletion, insertion, addition and/or inversion of bases. Note that the modification as used herein includes modifications by a mutation treatment with a mutagen or UV irradiation, or modifications by spontaneous mutation.

To screen transformants, it is preferable that the vectors have markers such as an ampicillin resistant gene. As such plasmids are commercially available expression vectors having potent promoters (a pUC-based vector (manufactured by Takara Shuzo, Co., Ltd.), pRROK-based vector (manufactured by Clonetech Laboratories, Inc.), pKK233-2 (manufactured by Clonetech Laboratories, Inc.) and so forth.

A recombinant DNA is obtained by ligating a DNA fragment to a vector DNA. In this case, a promoter, a gene encoding L-amino acid amide hydrolase or a fused protein consisting of an L-amino acid amide hydrolase and another protein, and depending on the case, a terminator are ligated in that order.

When Escherichia coli is transformed using the recombinant DNA and the resulting Escherichia coli is cultured, a peptide-forming enzyme or a fused protein consisting of the peptide-forming enzyme and another protein is expressed and produced. Although a strain that is normally used in the expression of a heterogeneous gene can be used as a host to be transformed, Escherichia coli strain JM109, for example, is preferable. Methods for carrying out transformation and methods for screening out transformants are described in Molecular Cloning, 2nd Edition, Cold Spring Harbor Press (1989) and other publications.

In the case of expressing a peptide-forming enzyme in the form of a fusion protein, the peptide-forming enzyme may be cleaved out using a restriction protease that uses a sequence not present in the peptide-forming enzyme, such as blood coagulation factor Xa or kallikrein, as the recognition sequence.

A medium normally used for culturing Escherichia coli, such as M9-casamino acid medium or LB medium, may be used as a production medium. In addition, culturing conditions and production induction conditions are suitably selected according to the marker of the vector used, promoter, type of host microbe and so forth.

The following method can be used to recover the peptide-forming enzyme or fused protein consisting of the peptide-forming enzyme and another protein. If the peptide-forming enzyme or its fused protein has been solubilized within the microbial cells, after recovering the microbial cells, the microbial cells are crushed or lysed so that they can be used as a crude enzyme liquid. Moreover, the peptide-forming enzyme or its fused protein can be purified prior to use by ordinary techniques such as precipitation, filtration or column chromatography as necessary. In this case, a purification method can also be used that uses an antibody of the peptide-forming enzyme or its fused protein.

In the case where protein inclusion bodies are formed, the inclusion bodies are solubilized with a denaturant. They may be solubilized together with the microbial cell protein. However, in consideration of the following purification procedure, the inclusion bodies are preferably taken out and then solubilized. Conventionally known methods may be used to recover the inclusion bodies from the microbial cells. For example, inclusion bodies can be recovered by crushing the microbial cells followed by centrifugal separation. Examples of denaturants capable of solubilizing inclusion bodies include guanidine hydrochloride (for example, 6 M, pH 5 to 8) and urea (for example, 8 M).

A protein having activity is regenerated by removing these denaturants by dialysis. A Tris-HCl buffer solution or a phosphate buffer solution and so forth may be used as the dialysis solution to be used in dialysis, and the concentration may be, for example, 20 mM to 0.5 M, while the pH may be, for example, 5 to 8.

The protein concentration during the regeneration step is preferably held to about 500 μg/ml or less. The dialysis temperature is preferably 5° C. or lower to inhibit the regenerated peptide-forming enzyme from undergoing self-crosslinking. Moreover, in addition to dialysis, dilution or ultrafiltration may be used to remove the denaturants, and it is expected that the activity can be regenerated regardless of whichever denaturant is used.

<2> Method of Producing α-L-aspartyl-L-phenylalanine-α-methyl Ester

The method of producing α-APM according to the present invention includes a first step of synthesizing α-L-aspartyl-L-phenylalanine-β-methyl ester according to the “<1> Method of producing α-L-aspartyl-L-phenylalanine-β-ester” and a second step of converting α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester.

Preferred conditions in the first step and the like are as described in the “<1> Method of producing α-L-aspartyl-L-phenylalanine-β-ester”. In addition, the second step can be carried out according to the known method and reference may be made to the method and preferred conditions described in, for example, Japanese Patent Publication No. H4-41155, etc. By the production method of α-APM according to the present invention, α-APM, which is important as a sweetener and the like, can be inexpensively produced at high yield.

EXAMPLES

Hereinafter, the present invention will be explained by examples. However, the present invention is not limited to these examples. In addition to confirmation by ninhydrin coloring of thin-film chromatograms (qualitative), quantitative determinations were made by the following high-performance liquid chromatography in order to assay products. Column: InertsiL ODS-2 (manufactured by GL Science, Inc.), eluate: aqueous phosphate solution containing 5.0 mM sodium 1-octanesulfonate (pH 2.1): methanol=100:15 to 50, flow rate: 1.0 mL/min, detection: 210 nanometers (nm).

Example 1 Microbes that Produce α-L-aspartyl-L-phenylalanine-β-methyl Ester

50 milliliters (“mL” or “ml”) of a medium (pH 7.0) containing 20 grams (“g”) of glycerol, 5 g of ammonium sulfate, 1 g of potassium dihydrogen phosphate, 3 g of dipotassium hydrogen phosphate, 0.5 g of magnesium sulfate, 10 g of yeast extract and 10 g of peptone in 1 liter (L) that was transferred to a 500 mL Sakaguchi flask and sterilized at 115° C. for 15 minutes (medium 1) was used to culture bacteria and actinomycetes shown in Table 1-1. A slant agar medium (pH 7.0) containing 5 g/L of glucose, 10 g/L of yeast extract, 10 g/L of peptone, 5 g/L of NaCl and 20 g/L of agar in the medium 1 was prepared and a microbe shown in Table 1 was cultured on this slant agar medium at 30° C. for 24 hours. Then, one loopful of the microbe was cultured in the medium 1 at 30° C. for 24 hours, followed by shake culturing at 30° C. and 120 strokes/min for 17 hours. After completion of the culturing, the microbial cells were separated from these culture liquids by centrifugation, and suspended in 0.1 M borate buffer (pH 9.0) containing 10 mM EDTA to 100 g/L as wet microbial cells.

To culture yeast shown in Table 1-1, 50 mL of a medium (pH 6.0) containing 10 g of glucose, 10 g of glycerol, 5 g of ammonium sulfate, 1 g of potassium dihydrogen phosphate, 3 g of dipotassium hydrogen phosphate, 0.5 g of magnesium sulfate, 5 g of yeast extract, 5 g of malt extract and 10 g of peptone in 1 L transferred to a 500-mL Sakaguchi flask and sterilized at 115° C. for 15 minutes (medium 2) was used. A slant agar medium (pH 6.0) containing 5 g/L of glucose, 5 g/L of yeast extract, 5 g/L of malt extract, 10 g/L of peptone, 5 g/L of NaCl and 20 g/L agar in the medium 2 was prepared and a yeast shown in Table 1 was cultured on the slant agar medium at 30° C. for 24 hours. Then, one loopful of the yeast was shake cultured at 30° C. for 24 hours in the medium 2 at 25° C. and 120 strokes/min for 17 hours. After completion of the culturing, the microbial cells were separated from these culture liquids by centrifugation, and suspended in 0.1 M borate buffer (pH 9.0) containing 10 mM EDTA to 100 g/L as wet microbial cells.

The microbes shown in Table 1-2 were cultured as follows. An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 1 g of tryptone, 1 g of yeast extract and 15 g of agar in 1 L of Daigo artificial sea water SP was used to culture Cellulophaga lytica NBRC 14961 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) or Flexithrix dorotheae NBRC 15987 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Cellulophaga lytica NBRC 14961 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) or Flexithrix dorotheae NBRC 15987 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured on this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

A sheep blood agar medium (Nisei Plate, Nisei Pharmaceutical) was used to culture Weeksella virosa NBRC 16016 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Weeksella virosa NBRC 16016 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured on this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 10 g of peptone, 2 g of yeast extract, 1 g of MgSO₄.7H₂O and 15 g of agar in 1 L of distilled water was used to culture Pedobacter heparinus NBRC 12017 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Pedobacter heparinus NBRC 12017 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured on this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 0.5 g of KNO₃, 0.1 g of sodium glycerophosphate, 1 g of trishydroxymethylaminomethane, 5 g of tryptone, 5 g of yeast extract, 15 g of agar and 1 ml of a trace element solution in 1 L of Daigo artificial sea water SP was used to culture Persicobacter diffluens NBRC 15940 ((Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) Note that the trace element solution contained 2.85 g of H₃BO₄, 1.8 g of MnCl₂.4H₂O, 1.36 g of FeSO₄.7H₂O, 26.9 mg of CuCl₂.2H₂O, 20.8 mg of ZnCl₂, 40.4 mg of CoCl₂.6H₂O, 25.2 mg of Na₂MoO₄.2H₂O, and 1.77 g of sodium tartrate). Microbial cells of Persicobacter diffluens NBRC 15940 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured on this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 3 g of bactocasitone, 1 g of yeast extract, 1.36 g of CaCl₂.2H₂O and 15 g of agar in 1 L of distilled water was used to culture Chitinophaga pinensis NBRC 15968 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Chitinophaga pinensis NBRC 15968 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured on this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 5 g of peptone, 1 g of yeast extract, 0.2 g of FeSO₄.7H2O and 15 g of agar in 1 L of Daigo artificial sea water SP was used to culture Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). Microbial cells of Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured on this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 1 g of peptone, 1 g of yeast extract, 1 g of glucose and 15 g of agar in 1 L of distilled water was used to culture Runella slithyformis ATCC 29530 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). Microbial cells of Runella slithyformis ATCC 29530 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured in this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 8.2, sterilized at 120° C. for 15 minutes) containing 0.2 g of nitrilotriacetic acid, 2 ml of a 0.03% FeCl₃ solution, 0.12 g of CaSO₄.2H₂O, 0.2 g of MgSO₄.7H₂O, 0.016 g of NaCl, 0.21 g of KNO₃, 1.4 g of NaNO₃, 0.22 g of Na₂HPO₄, 2 ml of trace element solution and 15 g of agar in 1 L of distilled water was used to culture Thermonema lapsum ATCC 43542 ((Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) it should be noted that the trace element solution contained 0.5 ml of H₂SO₄, 2.2 g of MnSO₄, 0.5 g of ZnSO₄, 0.5 g of H₃BO₃, 0.016 g of CuSO₄, 0.025 g of Na₂MoO₄ and 0.046 g of CoCl₂). Microbial cells of Thermonema lapsum ATCC 43542 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured on this medium at 60° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

Marine Agar 2216 (manufactured by Difco) was used to culture Gelidibacter algens ATCC 700364 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), Lewinella cohaerens ATCC 23123 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), or Salegentibacter salegens DSMZ 5424 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). In the case of Gelidibacter algens ATCC 700364 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) or Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), microbial cells of Gelidibacter algens ATCC 700364, or Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured on this medium at 10° C. for 72 hours were applied, followed by main culturing at 10° C. for 72 hours. In the case of Lewinella cohaerens ATCC 23123 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America), microbial cells of Lewinella cohaerens ATCC 23123 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours. In the case of Salegentibacter salegens DSMZ 5424 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany), microbial cells of Salegentibacter salegens DSMZ 5424 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) which was seed cultured in this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 0.8 g of NH₄Cl, 0.25 g of KH₂PO₄, 0.4 g of K₂HPO₄, 0.505 g of KNO₃, 15 mg of CaCl₂.2H₂O, 20 mg of MgCl₂.6H₂O, 7 mg of FeSO₄.7H₂O, 5 mg of Na₂SO₄, 5 mg of MnCl₂.4H₂O, 0.5 mg of H₃BO₃, 0.5 mg of ZnCl₂, 0.5 mg of CoCl₂.6H₂O, 0.5 mg of NiSO₄.6H₂O, 0.3 mg of CuCl₂.2H₂O, 10 mg of Na₂MoO₄.2H₂O, 0.5 g of yeast extract, 0.5 g of peptone, 0.5 g of casamino acid, 0.5 g of dextrose, 0.5 g of soluble starch, 0.5 g of sodium pyruvate, and 15 g of agar in 1 L of distilled water was used to culture Dyadobacter fermentans ATCC 700827 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). Microbial cells of Dyadobacter fermentans ATCC 700827 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured in this medium at 25° C. for 48 hours, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 2 g of tryptone, 0.5 g of meat extract, 0.5 g of yeast extract, 0.2 g of sodium acetate and 15 g of agar in 1 L of Daigo artificial sea water SP was used to culture Flammeovirga aprica NBRC 15941 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Flammeovirga aprica NBRC 15941 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured in this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 1 g of glucose, 1 g of peptone, 1 g of yeast extract, and 15 g of agar in 1 L of distilled water was used to culture Spirosoma linguale DSMZ 74 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) or Flectobacillus major DSMZ 103 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). Microbial cells of Spirosoma linguale DSMZ 74 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) or Flectobacillus major DSMZ 103 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) which was seed cultured on this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 0.5 g of tryptone, 0.5 g of yeast extract, 0.2 g of meat extract, 0.2 g of sodium acetate and 15 g of agar in 300 ml of distilled water and 700 ml of Daigo artificial sea water SP was used to culture Tenacibaculum maritimum ATCC 43398 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). Microbial cells of Tenacibaculum maritimum ATCC 43398 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured in this medium at 25° C. for 48 hours, followed by main culturing at 25° C. for 48 hours.

An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 2.5 g of yeast extract, 2.5 g of tryptone, 100 mg of nitrilotriacetic acid, 40 mg of CaSO₄.2H₂O, 200 mg of MgCl₂.6H₂O, 0.5 ml of 0.01M Fe citrate, 0.5 ml of a trace element solution, 100 ml of phosphate buffer, 900 ml of distilled water, and 28 g of agar in 1 L was used to culture Rhodothermus marinus DSMZ 4252 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). Note that the trace element solution contained 12.8 g of nitrilotriacetic acid, 1 g of FeCl₂.4H₂O, 0.5 g of MnCl₂.4H₂O, 0.3 g of CoCl₂.4H₂O, 50 mg of CuCl₂.2H₂O, 50 mg of Na₂MoO₄.2H₂O, 20 mg of H₃BO₃ and 20 mg of NiCl₂.6H₂O). Microbial cells of Rhodothermus marinus DSMZ 4252 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) which was seed cultured in this medium at 60° C. for 48 hours were applied on the same medium, followed by main culturing at 60° C. for 48 hours.

An agar solid medium (1.5% agar, pH 7.6, sterilized at 120° C. for 15 minutes) containing BACTO MARINE BROTH (DIFCO 2216) was used to culture Zobellia galactanivorans DSMZ 12802 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). This medium was applied with microbial cells of Zobellia galactanivorans DSMZ 12802 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 1.5 g of yeast extract, 2.5 g of peptone, 2 g of hexadecane, 17.7 g of NaCl, 0.48 g of KCl, 3.4 g of MgCl₂.6H₂O, 4.46 g of MgSO₄.7H₂O, 0.98 g of CaCl₂ and 15 g of agar in 1 L of distilled water was used to culture Muricauda ruestringenesis DSMZ 13258 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). Microbial cells of Muricauda ruestringenesis DSMZ 13258 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 3 g of casitone, 1 g of yeast extract, 1.36 g of CaCl₂.2H₂O and 15 g of agar in 1 L of distilled water was used to culture Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). Microbial cells of Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 3 g of casitone, 1 g of yeast extract, 1.36 g of CaCl₂.2H₂O, 5 g of cellobiose and 15 g of agar in 1 L of distilled water was used to culture Cytophaga hutchinsonii NBRC 15051 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Cytophaga hutchinsonii NBRC 15051 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.2, sterilized at 120° C. for 15 minutes) containing 10 g of peptone, 2 g of yeast extract, 0.5 g of MgSO₄.7H₂O, and 15 g of agar in 250 ml of distilled water and 750 ml of Daigo artificial sea water SP was used to culture Marinilabilia salmonicolor NBRC 15948 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan). Microbial cells of Marinilabilia salmonicolor NBRC 15948 (Depositary institution; the NITE Biological Resource Center of the National Institute of Technology and Evaluation, address of depositary institution; 5-8 Kazusa-Kamaashi 2-Chome, Kisarazu-shi, Chiba-ken, Japan) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.0, sterilized at 120° C. for 15 minutes) containing 0.5 g of KNO₃, 0.1 g of sodium glycerophosphate, 1 g of trishydroxymethylaminomethane, 2 g of tryptone, 2 g of yeast extract, 15 g of agar and 1 ml of a trace element solution in 1 L of Daigo artificial sea water SP was used to culture Saprospira grandis ATCC 23119 ((Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). Note that the trace element solution contained 2.85 g of H₃BO₄, 1.8 g of MnCl₂.4H₂O, 1.36 g of FeSO₄.7H₂O, 26.9 mg of CuCl₂.2H₂O, 20.8 mg of ZnCl₂, 40.4 mg of CoCl₂.6H₂O, 25.2 mg of Na₂MoO₄.2H₂O and 1.77 g of sodium tartrate). Microbial cells of Saprospira grandis ATCC 23119 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured in this medium at 30° C. for 48 hours were applied on the same medium, followed by main culturing at 30° C. for 48 hours.

An agar solid medium (pH 7.5, sterilized at 120° C. for 15 minutes) containing 27 mg of KH₂PO₄, 40 mg of K₂HPO₄, 40 mg of Na₂HPO₄.2H₂O, 50 mg of CaCl₂.2H₂O, 75 mg of MgSO₄.7H₂O, 5 mg of FeCl₃.6H₂O, 3 mg of MnSO₄.H₂O, 1.31 g of glutamic acid, 2.5 mg of Trypticase Soy Broth without glucose, 0.4 mg of thiamine, 0.01 mg of vitamin B12, 2 g of glucose, and 1 ml of a trace element solution in 1 L of distilled water was used to culture Haliscomenobacter hydrossis ATCC 27775 ((Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). Note that the trace element solution contained 0.1 g of ZnSO₄.7H₂O, 0.03 g of MnCl₂.4H₂O, 0.3 g of H₃BO₃, 0.2 g of CoCl₂.6H₂O, 0.01 g of CuCl₂.2H₂O, 0.02 g of NiCl₂.6H₂O and 0.03 g of Na₂MoO₄.H₂O). Microbial cells of Haliscomenobacter hydrossis ATCC 27775 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) which was seed cultured in this medium at 25° C. for 48 hours were applied on the same medium, followed by main culturing at 25° C. for 48 hours.

The thus obtained microbial cells were each collected from the agar medium, and suspended in 0.1 M borate buffer (pH 9.0) containing 10 mM EDTA to 100 g/L as wet microbial cells.

To 0.1 mL each of the microbial cell suspensions of these microbes was added 0.1 mL of 100 mM borate buffer (pH 9.0) containing 10 mM EDTA, 100 mM L-aspartic acid-α,β-dimethyl ester hydrochloride and 200 mM L-phenylalanine to make the total amount 0.2 mL. Then, reaction was carried out at 20° C. for 3 hours when the microbe shown in Table 1-1 was used or for 1 hour when the microbe shown in Table 1-2 was used. The amount (mM) of α-L-aspartyl-L-phenylalanine-β-methyl ester (α-AMP) produced is shown in Tables 1-1 and 1-2. Note that no β-AMP was detected in all the cases where the microbes were used.

TABLE 1-1 Microbe α-AMP (mM) Aeromonas hydrophila ATCC 13136 1.55 Azotobacter vinelandii IFO 3741 0.15 Alcaligenes faecalis FERM P-8460 0.37 Brevibacterium minutiferuna FERM BP-8277 0.10 Corynebacterium flavescens ATCC 10340 0.26 Escherichia coli FERM BP-8276 3.68 Empedobacter brevis ATCC 14234 6.31 Flavobacterium resinovorum ATCC 14231 0.62 Microbacterium arborescens ATCC 4348 0.08 Propionibacterium shermanii BERM BP-8100 3.41 Brevibacillus parabrevis ATCC 8185 0.08 Paenibacillus alvei IFO 14175 0.09 Pseudomonas fragi IFO 3458 0.84 Serratia grimesii ATCC 14460 0.47 Stenotrophomonas maltophilia ATCC 13270 0.18 Sphingobacterium sp. FERM BP-8124 5.97 Streptomyces lavendulae NRRL B-1305 0.89 Xanthomonas maltophilia FERM BP-5568 0.40 Williopsis saturnus IFO 0895 0.05 Candida magnoliae IFO 0705 0.26 Geotrichum amycelium CBS 152.25 0.19 Geotrichum amycelium IFO 0905 0.06 Saccharomyces unisporus IFO 0724 0.07 Torulaspora delbrueckii IFO 0422 0.04 Pichia ciferrii IFO 0905 0.06

TABLE 1-2 Microbe α-AMP (mM) Cellulophaga lytica NBRC 14961 tr Weeksella virosa NBRC 16016 tr Pedobacter heparinus NBRC 12017 0.07 Persicobacter diffluens NBRC 15940 tr Flexithrix dorotheae NBRC 15987 2.47 Chitinophaga pinensis NBRC 15968 0.08 Cyclobacterium marinum ATCC 25205 0.91 Runella slithyformis ATCC 29530 0.07 Thermonema lapsum ATCC 43542 tr Psychroserpens burtonensis ATCC 700359 0.09 Gelidibacter algens ATCC 700364 0.07 Dyadobacter fermentans ATCC 700827 0.04 Flammeovirga aprica NBRC 15941 0.08 Spirosoma linguale DSMZ 74 0.15 Flectobacillus major DSMZ 103 0.68 Tenacibaculum maritimum ATCC 43398 tr Rhodotermus marinus DSMZ 4252 0.06 Zobellia galactanivorans DSMZ 12802 0.42 Muricauda ruestringensis DSMZ 13258 0.51 Salegentibacter salegens DSMZ 5424 tr Taxeobacter gelupurpurascens DSMZ 11116 0.02 Cytophaga hutchinsonii NBRC 15051 tr Marinilabilia salmonicolor NBRC 15948 0.02 Lewinella cohaerens ATCC 23123 0.33 Saprospira grandis ATCC 23119 0.03 Haliscomenobacter hydrossis ATCC 27775 tr

Reference Example 1 Microbe that Produces β-L-aspartyl-L-phenyl-alanine-α-methyl Ester

Microbes shown in Table 2 were cultured similarly to the procedure in bacteria in Table 1 of Example 1. After completion of the culturing, the microbial cells were separated from these culture broths by centrifugation, and suspended in 0.1 M borate buffer (pH 9.0) containing 10 mM EDTA to 100 g/L as wet microbial cells. To 0.1 mL each of the microbial cell suspensions of these microbes was added 0.1 mL of 100 mM borate buffer (pH 9.0) containing 10 mM EDTA, 100 mM L-aspartic acid-α,β-dimethyl ester hydrochloride and 200 mM L-phenylalanine to make the total amount 0.2 ml, followed by reaction at 30° C. for 2 hours. The amount (mM) of β-L-aspartyl-L-phenylalanine-α-methyl ester (β-AMP) produced in this case is indicated in Table 2. Note that no α-AMP was detected in all the microbes.

TABLE 2 Microbe β-AMP (mM) Hafnia alvei ATCC 9760 0.30 Klebsiella pneumoniae ATCC 8308 0.26

Example 2 Purification of Enzyme from Empedobacter brevis

A 50 mL medium (pH 6.2) containing 5 grams (g) of glucose, 5 g of ammonium sulfate, 1 g of monopotassium phosphate, 3 g of dipotassium phosphate, 0.5 g of magnesium sulfate, 10 g of yeast extract and 10 g of peptone in 1 liter (L) was transferred to a 500 mL Sakaguchi flask and sterilized at 115° C. for 15 minutes. This medium was then inoculated with 2 milliliters (ml or mL) of Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) that had been cultured at 30° C. for 16 hours in the same medium, followed by shake culturing at 30° C. and 120 strokes/min for 16 hours.

Subsequently, the procedure after centrifugal separation was carried out either on ice or at 4° C. The obtained culture broth was centrifuged to collect microbial cells. After washing 16 g of the microbial cells with 50 mM Tris-HCl buffer (pH 8.0), they were suspended in 40 milliliters (ml or mL) of the same buffer and subjected to ultrasonic crushing treatment for 45 minutes at 195 watts. This ultrasonically crushed liquid was then centrifuged (10,000 rpm, 30 minutes) to remove the crushed cell fragments and obtain an ultrasonic crushed liquid supernatant. This ultrasonic crushed liquid supernatant was dialyzed overnight against 50 mM Tris-HCl buffer (pH 8.0) followed by removal of the insoluble fraction by ultracentrifugation (50,000 rpm, 30 minutes) to obtain a soluble fraction in the form of the supernatant liquid. The resulting soluble fraction was applied to a Q-Sepharose HP column (manufactured by Amersham) pre-equilibrated with Tris-HCl buffer (pH 8.0), and the active fraction was collected from the non-adsorbed fraction. This active fraction was dialyzed overnight against 50 mM acetate buffer (pH 4.5) followed by removal of the insoluble fraction by centrifugal separation (10,000 rpm, 30 minutes) to obtain a dialyzed fraction in the form of the supernatant liquid. This dialyzed fraction was then applied to a Mono S column (manufactured by Amersham) pre-equilibrated with 50 mM acetate buffer (pH 4.5) to elute enzyme at a linear concentration gradient of the same buffer containing 0 to 1 M NaCl. The fraction that had the lowest level of contaminating protein among the active fractions was applied to a Superdex 200 pg column (manufactured by Amersham) pre-equilibrated with 50 mM acetate buffer (pH 4.5) containing 1 M NaCl, and gel filtration was performed by allowing the same buffer (pH 4.5) containing 1 M NaCl to flow through the column to obtain an active fraction solution. As a result of performing these procedures, the peptide-forming enzyme used in the present invention was confirmed to have been uniformly purified based on the experimental results of electrophoresis. The enzyme recovery rate in the aforementioned purification process was 12.2% and the degree of purification was 707 times.

Example 3 Production of α-L-aspartyl-L-phenylalanine-β-methyl Ester Using Enzyme Fraction of Empedobacter brevis

10 microliters (μl) of Mono S fraction enzyme (about 20 U/ml) obtained in Example 2 was added to 190 μl of borate buffer (pH 9.0) containing 105.3 mM L-aspartic acid-α,β-dimethyl ester hydrochloride, 210.5 mM L-phenylalanine and 10.51 mM EDTA and reaction was carried out at 20° C. The course of production of α-L-aspartyl-L-phenylalanine-β-methyl ester (α-AMP) is shown in Table 3. Note that almost no formation of α-L-aspartyl-L-phenylalanine-D-methyl ester was confirmed in the enzyme-not-added lot.

Further, 10 μl of Mono S fraction enzyme (about 20 U/ml) obtained in Example 2 was added to 190 μl of borate buffer (pH 9.0) containing each of 105.3 mM L-aspartic acid-α-methyl ester hydrochloride and L-aspartic acid-β-methyl ester hydrochloride, 210.5 mM L-phenylalanine and 10.51 mM EDTA was added and reaction was carried out at 20° C. As a result, no formation of the corresponding peptides was observed.

TABLE 3 Reaction time (minute) Produced α-AMP (mM) 30 23.0 60 42.1 120 61.7

Example 4 Purification of Enzyme from Sphingobacterium sp

Sphingobacterium sp. strain FERM BP-8124 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit date: Jul. 22, 2002) was cultured in the same manner as that in Example 2 using the medium shown in Example 2. The following procedure after centrifugal separation was carried out either on ice or at 4° C. The obtained culture broth was centrifuged (10,000 rpm, 15 minutes) to collect microbial cells. After washing 2 g of the microbial cells with 20 mM Tris-HCl buffer (pH 7.6), they were suspended in 8 ml of the same buffer and subjected to ultrasonic crushing treatment for 45 minutes at 195 W. This ultrasonically crushed liquid was then centrifuged (10,000 rpm, 30 minutes) to remove the crushed cell fragments to obtain an ultrasonically crushed liquid supernatant. This ultrasonically crushed liquid supernatant was dialyzed overnight against 20 mM Tris-HCl buffer (pH 7.6) followed by removal of the insoluble fraction by ultracentrifugation (50,000 rpm, 30 minutes) to obtain a soluble fraction in the form of the supernatant liquid. The resulting soluble fraction was applied to a Q-Sepharose HP column (manufactured by Amersham) pre-equilibrated with Tris-HCl buffer (pH 7.6), and the active fraction was collected from the non-adsorbed fraction. This active fraction was dialyzed overnight against 20 mM acetate buffer (pH 5.0) followed by removal of the insoluble fraction by centrifugal separation (10,000 rpm, 30 minutes) to obtain a dialyzed fraction in the form of the supernatant liquid. This dialyzed fraction was then applied to an SP-Sepharose HP column (manufactured by Amersham) pre-equilibrated with 20 mM acetate buffer (pH 5.0) to obtain the active fraction in which enzyme was eluted at a linear concentration gradient of the same buffer containing 0 to 1 M NaCl.

Example 5 Production of α-L-aspartyl-L-phenylalanine-β-methyl Ester and α-L-aspartyl-L-phenylalanine-β-ethyl Ester Using Enzyme Fraction of Sphingobacterium sp

In the case of production of α-L-aspartyl-L-phenylalanine-β-methyl ester (α-AMP), 15 μl of concentrated solution of SP-Sepharose HP fraction (about 15 U/ml) obtained in Example 4 was added to 185 μl of borate buffer (pH 9.0) containing 108.1 mM L-aspartic acid-α,β-dimethyl ester hydrochloride, 216.2 mM L-phenylalanine and 10.8 mM EDTA and reaction was carried out at 20° C. Similarly, in the case of production of α-L-aspartyl-L-phenylalanine-β-ethyl ester (α-AEP), 10 μl of a concentrated solution of SP-Sepharose HP fraction (about 15 U/ml) obtained in Example 4 was added to 190 μl of borate buffer (pH 9.0) containing 52.6 mM L-aspartic acid-α,β-diethyl ester hydrochloride, 105.2 mM L-phenylalanine and 10.8 mM EDTA and reaction was carried out at 20° C. The course of formation of AMP or AEP is shown in Table 4. Note that almost no formation of AMP or AEP was confirmed in the enzyme-not-added lot. For formation of AEP, numerical values obtained by using a standard product of AMP are described.

TABLE 4 Reaction Produced Produced time (minute) α-AMP (mM) α-AEP (mM) 30 25.8 7.5 60 40.7 13.3 120 56.0 20.6 180 61.8 —

Example 6 Isolation of Peptide-Forming Enzyme Gene Derived from Empedobacter brevis

Hereinafter, isolation of a peptide-forming enzyme gene will be explained. Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) was used as the microbe. In isolating the gene, Escherichia coli JM-109 was used as a host while pUC118 was used as a vector.

(1) Production of PCR Primer Based on Determined Internal Amino Acid Sequence

A mixed primer having the base sequences indicated in SEQ ID NO.: 3 and SEQ ID NO: 4, respectively, was produced based on the amino acid sequences (SEQ ID NOs: 1 and 2) determined according to the Edman's decomposition method from the digestion product of lysyl endopeptidase of a peptide-forming enzyme derived from the Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002).

(2) Acquisition of Microbial Cells

Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) was cultured at 30° C. for 24 hours on a CM2G agar medium (containing glucose at 50 g/l, yeast extract at 10 g/l, peptone at 10 g/l, sodium chloride at 5 g/l, and agar at 20 g/l, pH 7.0). One loopful of the resulting microbial cells was inoculated into a 500 ml Sakaguchi flask containing 50 ml of a CM2G liquid medium (the aforementioned medium excluding agar) followed by shake culturing at 30° C.

(3) Acquisition of Chromosomal DNA from Microbial Cells

50 ml of culture broth was centrifuged (12,000 rpm, 4° C., 15 minutes) to collect the microbial cells. Then, a chromosomal DNA was acquired from the microbial cells using the QIAGEN Genomic-Tip System (Qiagen) based on the procedure described in the manual therefor.

(4) Acquisition of DNA Fragment Containing Part of Peptide-Forming Enzyme Gene by PCR

A DNA fragment containing a portion of the peptide-forming enzyme gene derived from Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) was acquired by the PCR method using LA-Taq (manufactured by Takara Shuzo). A PCR reaction was then carried out on a chromosomal DNA acquired from Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) using the primers having the base sequences of SEQ ID NOs: 3 and 4.

The PCR reaction was carried out for 30 cycles under the following conditions using the Takara PCR Thermal Cycler PERSONAL (manufactured by Takara Shuzo).

94° C. 30 seconds 52° C. 1 minute 72° C. 1 minute

After completion of the reaction, 3 μl of the reaction liquid was applied to 0.8% agarose electrophoresis. As a result, it was verified that a DNA fragment of about 1.5 kilobases (kb) was amplified.

(5) Cloning of Peptide-Forming Enzyme Gene from Gene Library

In order to acquire the entire length of peptide-forming enzyme gene in full-length, Southern hybridization was carried out using the DNA fragment amplified in the PCR procedure as a probe. The procedure for Southern hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The approximately 1.5 kb DNA fragment amplified by the PCR procedure was isolated by 0.8% agarose electrophoresis. The target band was then cut out and purified. This The DNA fragment was labeled with probe digoxinigen using DIG High Prime (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor using DIG High Prime (manufactured by Boehringer-Mannheim).

After completely digesting the chromosomal DNA of Empedobacter brevis acquired in the step (3) of the present Example 6 by reacting at 37° C. for 16 hours with restriction enzyme HindIII, the resultant was electrophoresed with on 0.8% agarose gel. The electrophoresed chromosomal DNA was blotted onto a positively charged Nylon membrane filter (manufactured by Roche Diagnostics) from the agarose gel after the electrophoresis, followed by treatments consisting of alkaline denaturation, neutralization and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 50° C. for 1 hour, the probe labeled with digoxinigen prepared as described above was added and hybridization was carried out at 50° C. for 16 hours. Subsequently, the filter was washed for 20 minutes at room temperature with 2×SSC containing 0.1% SDS. Moreover, the filter was additionally washed twice at 65° C. for 15 minutes with 0.1×SSC containing 0.1% SDS.

Detection of bands that hybridized with the probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim). As a result, a roughly 4 kb band was able to be detected that hybridized with the probe.

Then, 5 μg of the chromosomal DNA prepared in the step (3) of the present Example 6 was completely digested with HindIII. A roughly 4 kb of DNA was separated by 0.8% agarose gel electrophoresis, followed by purification of the DNA using the Gene Clean II Kit (manufactured by Funakoshi) and dissolving the DNA in 10 μl of TE. 4 μl of this product was then mixed with pUC118 HindIII/BAP (manufactured by Takara Shuzo) and a ligation reaction was carried out using the DNA Ligation Kit Ver. 2 (manufactured by Takara Shuzo). 5 μl of the ligation reaction mixture and 100 μl of competent cells of Escherichia coli JM109 (manufactured by Toyobo) were mixed to transform the Escherichia coli. This was then applied to a suitable solid medium to produce a chromosomal DNA library.

To acquire the entire full-length of peptide-forming enzyme gene, the chromosomal DNA library was screened by colony hybridization using the aforementioned probe. The procedure for colony hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The colonies of the chromosomal DNA library were transferred to a Nylon membrane filter (Nylon Membrane for Colony and Plaque Hybridization, (manufactured by Roche Diagnostics) followed by treatments consisting of alkali denaturation, neutralization and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the aforementioned probe labeled with digoxinigen was added, followed by hybridization at 50° C. for 16 hours. Subsequently, the filter was washed for 20 minutes at room temperature with 2×SSC containing 0.1% SDS. Moreover, the filter was additionally washed twice at 65° C. for 15 minutes with 0.1×SSC containing 0.1% SDS.

Detection of colonies that hybridized with the labeled probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the explanation described in the manual therefor using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim). As a result, two strains of colonies were verified to hybridize with the labeled probe.

(6) Base Sequence of Peptide-Forming Enzyme Gene Derived from Empedobacter brevis

Plasmids possessed by Escherichia Coli JM109 were prepared from the aforementioned two strains of microbial cells that were verified to hybridize with the labeled probe using the Wizard Plus Minipreps DNA Purification System (manufactured by Promega) to and the base sequence of a portion where hybridization with the probe occurred and nearby was determined. The sequencing reaction was carried out using the CEQ DTCS-Quick Start Kit (manufactured by Beckman-Coulter) based on the procedure described in the manual therefor. In addition, electrophoresis was carried out using the CEQ 2000-XL (manufactured by Beckman-Coulter).

As a result, it was verified that an open reading frame that encodes a protein containing the internal amino acid sequences of the peptide-forming enzyme (SEQ ID NOs: 1 and 2) did exist, thereby confirming that the open reading frame was a gene encoding the peptide-forming enzyme. The base sequence of the full-length of the peptide-forming enzyme genes along with the corresponding amino acid sequences is shown in SEQ ID NO: 5 of the Sequence Listing. As a result of analysis on the homology of the resulting open reading frame with the BLASTP program, homology was discovered between the two enzymes; it showed with a homology of 34% as at the amino acid sequence level exhibited with the α-amino acid ester hydrolase of Acetobacter pasteurianus (see Appl. Environ. Microbiol., 68(1), 211-218 (2002), and a homology of 26% at the amino acid sequence level exhibited with the glutaryl-7ACA acylase of Brevibacillus laterosporum (see J. Bacteriol., 173(24), 7848-7855 (1991).

(7) Expression of Peptide-Forming Enzyme Gene Derived from Empedobacter brevis in Escherichia coli

A target gene region on the promoter region of the trp operon on the chromosomal DNA of Escherichia coli W3110 was amplified by carrying out PCR using the oligonucleotides indicated in SEQ ID NOs: 7 and 8 as primers, and the resulting DNA fragments were ligated to a pGEM-Teasy vector (manufactured by Promega). E. coli JM109 was then transformed in this ligation solution, and those strains having the target plasmid in which the direction of the inserted trp promoter is inserted in the opposite to the orientation from of the lac promoter were selected from ampicillin-resistant strains. Next, a DNA fragment containing the trp promoter obtained by treating this plasmid with EcoO109I/EcoRI was ligated to an EcoO109I/EcoRI treatment product of pUC19 (manufactured by Takara). Escherichia coli JM109 was then transformed with this ligation solution and those strains having the target plasmid were selected from ampicillin-resistant strains. Next, a DNA fragment obtained by treating this plasmid with HindIII/PvuII was ligated with to a DNA fragment containing an rrnB terminator obtained by treating pKK223-3 (manufactured by Amersham Pharmacia) with HindIII/HincII. E. coli JM109 was then transformed with this ligation solution, strains having the target plasmid were selected from ampicillin-resistant strains, and the plasmid was designated as pTrpT.

The target gene was amplified by PCR using the chromosomal DNA of Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) as a template and the oligonucleotides indicated in SEQ ID NO: 9 and 10 as primers. This DNA fragment was then treated with NdeI/PstI, and the resulting DNA fragment was ligated with the NdeI/PstI treatment product of pTrpT. Escherichia coli JM109 was then transformed with this ligation solution, those strains having the target plasmid were selected from ampicillin-resistant strains, and this plasmid was designated as pTrpT_Gtg2.

Escherichia coli JM109 having pTrpT_Gtg2 was seed cultured at 30° C. for 24 hours in LB medium containing 100 mg/l of ampicillin. 1 ml of the resulting culture broth was seeded in a 500 ml Sakaguchi flask containing 50 ml of a medium (D glucose at 2 g/l, yeast extract at 10 g/l, casamino acids at 10 g/l, ammonium sulfate at 5 g/l, potassium dihydrogen phosphate at 3 g/l, dipotassium hydrogen phosphate at 1 g/l, magnesium sulfate heptahydrate at 0.5 g/l, and ampicillin at 100 mg/l), followed by culturing at 25° C. for 24 hours. The culture broth had an α-L-aspartyl-phenylalanine-β-methyl ester forming activity of 0.11 Upper 1 ml of culture broth and it was verified that the cloned gene was expressed by E. coli. Furthermore, no activity was detected for a transformant in which only pTrpT had been introduced as a control.

Prediction of Signal Sequence

When the amino acid sequence of SEQ ID NO: 6 described in the Sequence Listing was analyzed with the Signal P v 1.1 program (see Protein Engineering, Vol. 12, No. 1, pp. 3-9, 1999), it was predicted that amino acids numbers 1 to 22 function as a signal that is secreted into the periplasm, while the mature protein was estimated to be downstream of amino acid number 23.

Verification of Secretion

Escherichia coli JM109, having pTrpT_Gtg2, was seed cultured at 30° C. for 24 hours in LB medium containing 100 mg/l of ampicillin. 1 ml of the resulting culture broth was seeded into a 500 ml Sakaguchi flask containing 50 ml of medium (glucose at 2 g/l, yeast extract at 10 g/l, casamino acids at 10 g/l, ammonium sulfate at 5 g/l, potassium dihydrogen phosphate at 3 g/l, dipotassium hydrogen phosphate at 1 g/l, magnesium sulfate heptahydrate at 0.5 g/l, and ampicillin at 100 mg/l), followed by final culturing at 25° C. for 24 hours to obtain cultured microbial cells.

The cultured microbial cells were fractionated into a periplasm fraction and a cytoplasm fraction by an osmotic pressure shock method using a 20 grams/deciliter (g/dl) sucrose solution. The microbial cells immersed in the 20 g/dl sucrose solution were immersed in a 5 mM aqueous MgSO₄ solution. The centrifuged supernatant was named a periplasm fraction (“Pe”). In addition, the centrifuged sediment was re-suspended and subjected to ultrasonic crushing. The resultant was named a cytoplasm fraction (“Cy”). The activity of glucose 6-phosphate dehydrogenase, which is known to be present in the cytoplasm, was used as an indicator to verify that the cytoplasm had been separated. This measurement was carried out by adding a suitable amount of enzyme to a reaction solution at 30° C. containing 1 mM glucose 6-phosphate, 0.4 mM NADP, 10 mM MgSO₄, and 50 mM Tris-Cl (pH 8), followed by measurement of absorbance at 340 nm to measure production of NADPH.

The amounts of enzymes of in the periplasm fraction and the cytoplasm fraction when the activity of a separately prepared cell-free extract was assigned a value of 100% are shown in FIG. 1. That glucose 6-phosphate dehydrogenase activity did not mix in the periplasm fraction indicates that the periplasm fraction did not mix in the cytoplasm fraction. About 60% of the α-L-aspartyl-L-phenylalanine-β-methyl ester (α-AMP) forming activity was recovered in the periplasm fraction, and it was verified that the Ala-Gln-forming enzyme was secreted into the periplasm as predicted from the amino acid sequence using the Signal P v 1.1 program.

Example 7 Isolation of Peptide-Forming Enzyme Gene Derived from Sphingobacterium sp

Hereinafter, isolation of a peptide-forming enzyme gene is described.

The microbe used was Sphingobacterium sp. strain FERM BP-8124 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit date: Jul. 22, 2002). For the isolation of the gene, Escherichia coli DH5α was used as a host, and pUC118 was used as a vector.

(1) Acquisition of Microbial Cells

Sphingobacterium sp. strain FERM BP-8124 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit date: Jul. 22, 2002) was cultured for 24 hours at 25° C. on a CM2G agar medium (containing glucose at 50 g/l, yeast extract at 10 g/l, peptone at 10 g/l, sodium chloride at 5 g/l, and agar at 20 g/l, pH 7.0). One loopful of the resulting microbial cells was inoculated into a 500 ml Sakaguchi flask containing 50 ml of CM2G liquid medium (the aforementioned medium excluding agar) followed by shake culturing at 25° C.

(2) Acquisition of Chromosomal DNA from Microbial Cells

50 ml of culture broth was centrifuged (12,000 rpm, 4° C., 15 minutes) to collect the microbial cells. A chromosomal DNA was then acquired from the microbial cells using the Qiagen Genomic-Tip System (Qiagen) based on the procedure described in the manual therefor.

(3) Acquisition of Probe DNA Fragment by PCR

A DNA fragment containing a portion of the peptide-forming enzyme gene derived from Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) was acquired by the PCR method using LA-Taq (manufactured by Takara Shuzo). A PCR reaction was then carried out on the chromosomal DNA acquired from Empedobacter brevis strain FERM BP-8113 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit transfer date: Jul. 8, 2002) using primers having the base sequences of SEQ ID NOs: 3 and 4.

The PCR reaction was carried out using the Takara PCR Thermal Cycler—PERSONAL (Takara Shuzo) for 30 cycles under the following conditions.

94° C. 30 seconds 52° C. 1 minute 72° C. 1 minute

After completion of the reaction, 3 μl of reaction liquid was applied to 0.8% agarose electrophoresis. As a result, it was verified that a DNA fragment of about 1.5 kb was amplified.

(4) Cloning of Peptide-Forming Enzyme Gene from Gene Library

In order to acquire the full-length peptide-forming enzyme gene, Southern hybridization was carried out using the DNA fragment amplified in the aforementioned PCR procedure as a probe. The operations of Southern hybridization are explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The approximately 1.5 kb DNA fragment amplified by the aforementioned PCR procedure was separated by 0.8% agarose electrophoresis. The target band was then cut out and purified. This DNA fragment was labeled with probe digoxinigen using DIG High Prime (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor.

After allowing the chromosomal DNA of Sphingobacterium sp. acquired in the step (2) of the present Example 7 to react with restriction enzyme SacI at 37° C. for 16 hours to completely digest the DNA, the resultant was electrophoresed on 0.8% agarose gel. From the agarose gel after the electrophoresis, the electrophoresed chromosomal DNA was blotted onto a positively charged Nylon membrane filter (manufactured by Roche Diagnostics), followed by treatments consisting of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the digoxinigen-labeled probe prepared as described above was added and hybridization was carried out at 37° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of bands that hybridized with the probe was carried out using the DIG Nucleotide Detection Kit (Boehringer-Mannheim) based on the procedure described in the manual therefor. As a result, a roughly 3 kb band was successfully detected that hybridized with the probe.

5 μg of the chromosomal DNA prepared in the step (2) of the present Example 7 was completely digested with SacI. About 3 kb of a DNA was separated by 0.8% agarose gel electrophoresis, the DNA was purified using the Gene Clean II Kit (manufactured by Funakoshi), and dissolved in 10 μl of TE. 4 μl of the resulting solution and pUC118 treated with alkaline phosphatase (E. coli C75) at 37° C. for 30 minutes and at 50° C. for 30 minutes, after reaction with SacI at 37° C. for 16 hours to completely digest, were mixed and a ligation reaction was carried out using the DNA Ligation Kit Ver. 2 (manufactured by Takara Shuzo). 5 μl of this ligation reaction liquid and 100 μl of competent cells of Escherichia coli DH5α (manufactured by Takara Shuzo) were mixed to transform the Escherichia coli. This was then applied to a suitable solid medium to produce a chromosomal DNA library.

To acquire full-length peptide-forming enzyme gene, the chromosomal DNA library was screened by colony hybridization using the aforementioned probe. The procedure for colony hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The colonies of the chromosomal DNA library were transferred to a Nylon membrane filter (Nylon Membrane for Colony and Plaque Hybridization, manufactured by Roche Diagnostics), followed by treatments of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the aforementioned digoxinigen-labeled probe was added, followed by hybridization at 37° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of colonies that hybridized with the labeled probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the explanation described in the manual therefor. As a result, six strains of colonies were verified to have hybridized with the labeled probe.

(5) Base Sequence of Peptide-Forming Enzyme Gene Derived from Sphingobacterium sp.

Plasmids possessed by Escherichia coli DH5α were prepared from the six strains of microbial cells that were verified to have hybridized with the labeled probe using the Wizard Plus Minipreps DNA Purification System (manufactured by Promega) to determine the base sequence of a portion where hybridization with the probe occurred and nearby was determined. The sequencing reaction was carried out using the CEQ DTCS-Quick Start Kit (manufactured by Beckman-Coulter) based on the procedure described in the manual therefor. In addition, electrophoresis was carried out using the CEQ 2000-XL (manufactured by Beckman-Coulter).

As a result, it revealed that an open reading frame that encodes peptide-forming enzyme did exist. The full-length base sequence of the peptide-forming enzyme gene derived from Sphingobacterium sp. along with the corresponding amino acid sequence is shown in SEQ ID NO: 11. Peptide-forming enzyme derived from Sphingobacterium sp. exhibited a homology of 63.5% at the amino acid sequence level to the peptide-forming enzyme derived from Empedobacter brevis (as determined using the BLASTP program).

(6) Expression of Peptide-Forming Enzyme Gene Derived from Sphingobacterium sp. in Escherichia coli

The target gene was amplified by PCR using the chromosomal DNA of Sphingobacterium sp. FERM BP-8124 (Depositary institution: the independent administrative corporation, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address of depositary institution: Chuo Dai-6, 1-1 Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, Japan, International deposit date: Jul. 22, 2002) as a template and the oligonucleotides shown in SEQ ID NOs: 13 and 14 as primers. This DNA fragment was treated with NdeI/XbaI, and the resulting DNA fragment and an NdeI/XbaI treatment product of pTrpT were ligated. Escherichia coli JM109 was then transformed with this ligation solution, and strains having the target plasmid were selected from ampicillin-resistant strains. The plasmid was designated as pTrpT_Sm_aet.

Escherichia coli JM109 having pTrpT_Sm_aet was cultured at 25° C. for 20 hours by inoculating one loopful thereof into an ordinary test tube containing 3 ml of a medium (glucose at 2 g/l, yeast extract at 10 g/l, casamino acids at 10 g/l, ammonium sulfate at 5 g/l, potassium dihydrogen phosphate at 3 g/l, dipotassium hydrogen phosphate at 1 g/l, magnesium sulfate heptahydrate at 0.5 g/l and ampicillin at 100 mg/l). It was verified that a cloned gene having an α-AMP production activity of 0.53 Upper ml of culture broth was expressed by Escherichia coli. Furthermore, no activity was detected for a transformant containing only pTrpT used as a control.

Prediction of Signal Sequence

When the amino acid sequence of SEQ ID NO: 12 described in the Sequence Listing was analyzed with the Signal P v 1.1 program (Protein Engineering, Vol. 12, No. 1, pp. 3-9, 1999), it was predicted that amino acids numbers 1 to 20 function as a signal that is secreted into the periplasm, while the mature protein was estimated to be downstream of amino acid number 21.

Confirmation of Signal Sequence

One loopful of Escherichia coli JM109, having pTrpT_Sm_aet, was inoculated into ordinary test tubes containing 50 ml of a medium (glucose at 2 g/l, yeast extract at 10 g/l, casamino acids at 10 g/l, ammonium sulfate at 5 g/l, potassium dihydrogen phosphate at 3 g/l, dipotassium hydrogen phosphate at 1 g/l, magnesium sulfate heptahydrate at 0.5 g/l and ampicillin at 100 mg/l) and main culturing was performed at 25° C. for 20 hours.

Hereinafter, procedures after centrifugal separation were carried out either on ice or at 4° C. After completion of the culturing, the microbial cells were separated from the culture broth by centrifugation, washed with 100 mM phosphate buffer (pH 7), and then suspended in the same buffer. The microbial cells were then subjected to ultrasonic crushing treatment for 20 minutes at 195 W, the ultrasonic crushed liquid was centrifuged (12,000 rpm, 30 minutes) to remove the crushed cell fragments and obtain a soluble fraction. The resulting soluble fraction was applied to a CHT-II column manufactured by Biorad) pre-equilibrated with 100 mM phosphate buffer (pH 7), and enzyme was eluted at a linear concentration gradient with 500 mM phosphate buffer. A solution obtained by mixing the active fraction with 5 time volumes of 2 M ammonium sulfate and 100 mM phosphate buffer was applied to a Resource-PHE column (manufactured by Amersham) pre-equilibrated with 2 M ammonium sulfate and 100 mM phosphate buffer, and an enzyme was eluted at a linear concentration gradient by 2 to 0 M ammonium sulfate to obtain an active fraction solution. As a result of these procedures, it was verified that the peptide-forming enzyme was electrophoretically uniformly purified.

When the amino acid sequence of the aforementioned peptide-forming enzyme was determined by Edman's decomposition method, the amino acid sequence of SEQ ID NO: 15 was acquired, and the mature protein was verified to be downstream of amino acid number 21 as was predicted by the SignalP v 1.1 program.

Example 8 Isolation of Peptide-Forming Enzyme Gene Derived from Pedobacter heparinus IFO 12017

Hereinafter, isolation of a peptide-forming enzyme gene is described. The microbe used is Pedobacter heparinus IFO 12017 (Depositary institution; the Institute of Fermentation, Osaka, address of the depositary institution; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan). For the isolation of the gene, Escherichia coliJM109 was used as a host, and pUC118 was used as a vector.

(1) Acquisition of Microbial Cells

Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan) was cultured for 24 hours at 25° C. on a CM2G agar medium (containing glucose at 50 g/l, yeast extract at 10 g/l, peptone at 10 g/l, sodium chloride at 5 g/l, and agar at 20 g/l, pH 7.0). One loopful of the resulting microbial cells was inoculated into a 500 ml Sakaguchi flask containing 50 ml of CM2G liquid medium (the aforementioned medium excluding agar) followed by shake culturing at 25° C.

(2) Acquisition of Chromosomal DNA from Microbial Cells

50 ml of the culture broth was centrifuged (12,000 rpm, 4° C., 15 minutes) to collect the microbial cells. A chromosomal DNA was then acquired from the microbial cells using the Qiagen Genomic-Tip System (Qiagen) based on the procedure described in the manual therefor.

(3) Acquisition of Probe DNA Fragment by PCR

A DNA fragment containing a portion of the peptide-forming enzyme gene derived from Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan) was acquired by the PCR method using LA-Taq (manufactured by Takara Shuzo). A PCR reaction was then carried out on the chromosomal DNA acquired from Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan) using primers having the base sequences of SEQ ID NOs: 15 and 16. The approximately 1 kb DNA fragment amplified by the PCR procedure was isolated by 0.8% agarose electrophoresis. The target band was then cut out and purified. The DNA fragment was labeled with probe digoxinigen using DIG High Prime (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor.

(4) Cloning of Peptide-Forming Enzyme Gene from Gene Library

To acquire the full-length peptide-forming enzyme gene, Southern hybridization was carried out using the DNA fragment amplified in the aforementioned PCR procedure as a probe. The operations of Southern hybridization are explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

After allowing the chromosomal DNA of Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan) to react with restriction enzyme HindIII at 37° C. for 16 hours to completely digest the DNA, the resultant was electrophoresed on 0.8% agarose gel. From the agarose gel after the electrophoresis, the electrophoresed chromosomal DNA was blotted onto a positively charged Nylon membrane filter (manufactured by Roche Diagnostics), followed by treatments consisting of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 50° C. for 1 hour, the digoxinigen-labeled probe prepared as described above was added and hybridization was carried out at 50° C. for 16 hours, Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of bands that hybridized with the probe was carried out using the DIG Nucleotide Detection Kit (Boehringer-Mannheim) based on the procedure described in the manual therefor. As a result, a roughly 5 kb band was successfully detected that hybridized with the probe.

5 μg of the chromosomal DNA of Pedobacter heparinus IFO 12017 was completely digested with HindIII. About 5 kb of a DNA was separated by 0.8% agarose gel electrophoresis, the DNA was purified using the Gene Clean II Kit (manufactured by Funakoshi), and dissolved in 10 μl of TE. 4 μl of the resulting solution and pUC118 HindIII/BAP were mixed were mixed and a ligation reaction was carried out using the DNA Ligation Kit Ver. 2 (manufactured by Takara Shuzo). 5 μl of this ligation reaction liquid and 100 μl of competent cells of Escherichia coli JM109 (manufactured by Takara Shuzo) were mixed to transform the Escherichia coli. This was then applied on a suitable solid medium to produce a chromosomal DNA library.

To acquire a full-length peptide-forming enzyme gene, the chromosomal DNA library was screened by colony hybridization using the aforementioned probe. The procedure for colony hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The colonies of the chromosomal DNA library were transferred to a Nylon membrane filter, Nylon Membrane for Colony and Plaque Hybridization (manufactured by Roche Diagnostics), followed by treatments of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the aforementioned digoxinigen-labeled probe was added, followed by hybridization at 37° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of colonies that hybridized with the labeled probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the explanation described in the manual therefor. As a result, one strain whose colony hybridized with the labeled probe was observed.

(5) Base Sequence of Peptide-Forming Enzyme Gene Derived from Pedobacter heparinus IFO 12017

Plasmids possessed by Escherichia coli JM109 were prepared from the strain that was verified to have hybridized with the labeled probe and the base sequence of a portion where hybridization with the probe occurred and nearby was determined. The sequencing reaction was carried out using the CEQ DTCS-Quick Start Kit (manufactured by Beckman-Coulter) based on the procedure described in the manual therefor. In addition, electrophoresis was carried out using the CEQ 2000-XL (manufactured by Beckman-Coulter).

As a result, it revealed that an open reading frame that encodes peptide-forming enzyme did exist. The full-length base sequence of the peptide-forming enzyme gene derived from Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan) along with the corresponding amino acid sequence is shown in SEQ ID NO: 17.

Example 9 Expression of Peptide-Forming Enzyme Gene Derived from Pedobacter heparinus IFO 12017 in Escherichia coli

The target gene was amplified by PCR using the chromosomal DNA of Pedobacter heparinus IFO 12017 (Depositary institution: the Institute of Fermentation, Osaka; 2-17-85 Jusanbon-cho, Yodogawa-ku, Osaka-shi, Japan) as a template and the oligonucleotides shown in SEQ ID NOs: 19 and 20 as primers. This DNA fragment was treated with NdeI/HindIII, and the resulting DNA fragment and an NdeI/HindIII treatment product of pTrpT were ligated. Escherichia coli JM109 was then transformed with this ligation solution, and strains having the target plasmid were selected from ampicillin-resistant strains. The plasmid was designated as pTrpT_Ph_aet.

One loopful of Escherichia coli JM109 having pTrpT_Ph_aet was inoculated in an ordinary test tube containing 3 ml of a medium (glucose at 2 g/l, yeast extract at 10 g/l, casamino acids at 10 g/l, ammonium sulfate at 5 g/l, potassium dihydrogen phosphate at 3 g/l, dipotassium hydrogen phosphate at 1 g/l, magnesium sulfate heptahydrate at 0.5 g/l and ampicillin at 100 mg/l) and main culturing was performed at 25° C. for 20 hours. It was verified that the cultured broth had an α-AMP production activity of 0.01 Upper ml of culture broth so that it was verified that the cloned gene was expressed in Escherichia coli. Furthermore, no activity was detected in the transformant containing only pTrpT used as a control.

Example 10 Isolation of Peptide-Forming Enzyme Gene Derived from Taxeobacter gelupurpurascens DSMZ 11116

Hereinafter, isolation of a peptide-forming enzyme gene is described. The microbe used is Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures); address of the depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany). For the isolation of the gene, Escherichia coli JM109 was used as a host, and pUC118 was used as a vector.

(1) Acquisition of Microbial Cells

Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) was cultured for 24 hours at 25° C. on a CM2G agar medium (containing glucose at 50 g/l, yeast extract at 10 g/l, peptone at 10 g/l, sodium chloride at 5 g/l, and agar at 20 g/l, pH 7.0). One loopful of the resulting microbial cells was inoculated into a 500 ml Sakaguchi flask containing 50 ml of CM2G liquid medium (the aforementioned medium excluding agar) followed by shake culturing at 25° C.

(2) Acquisition of Chromosomal DNA from Microbial Cells

50 ml of the culture broth was centrifuged (12,000 rpm, 4° C., 15 minutes) to collect the microbial cells. A chromosomal DNA was then acquired from the microbial cells using the Qiagen Genomic-Tip System (Qiagen) based on the procedure described in the manual therefor.

(3) Acquisition of Probe DNA Fragment by PCR

A DNA fragment containing a portion of the peptide-forming enzyme gene derived from Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) was acquired by the PCR method using LA-Taq (manufactured by Takara Shuzo). A PCR reaction was then carried out on the chromosomal DNA acquired from Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) using primers having the base sequences of SEQ ID NOs: 21 and 16. The approximately 1 kb DNA fragment amplified by the PCR procedure was isolated by 0.8% agarose electrophoresis. The target band was then cut out and purified. The DNA fragment was labeled with probe digoxinigen using DIG High Prime (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor.

(4) Cloning of Peptide-Forming Enzyme Gene from Gene Library

To acquire the full-length peptide-forming enzyme gene, Southern hybridization was carried out using the DNA fragment amplified in the aforementioned PCR procedure as a probe. The operations of Southern hybridization are explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

After allowing the chromosomal DNA of Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) to react with restriction enzyme PstI at 37° C. for 16 hours to completely digest the DNA, the resultant was electrophoresed on 0.8% agarose gel. From the agarose gel after the electrophoresis, the electrophoresed chromosomal DNA was blotted onto a positively charged Nylon membrane filter (manufactured by Roche Diagnostics), followed by treatments consisting of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 50° C. for 1 hour, the digoxinigen-labeled probe prepared as described above was added and hybridization was carried out at 50° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of bands that hybridized with the probe was carried out using the DIG Nucleotide Detection Kit (Boehringer-Mannheim) based on the procedure described in the manual therefor. As a result, a roughly 5 kb band was successfully detected that hybridized with the probe.

5 μg of the chromosomal DNA of Taxeobacter gelupurpurascens DSMZ 11116 (Depositary institution; the Deutche Sammlung von Mikroorganismen und Zellkulturen GmbH (German Collection of Microbes and Cell Cultures, Address of Depositary institution; Mascheroder Weg 1b, 38124 Braunschweig, Germany) was completely digested with PstI. About 5 kb of a DNA was separated by 0.8% agarose gel electrophoresis, the DNA was purified using the Gene Clean II Kit (manufactured by Funakoshi), and dissolved in 10 μl of TE. 4 μl of the resulting solution and pUC118 PstI/BAP (manufactured by Takara Shuzo) were mixed were mixed and a ligation reaction was carried out using the DNA Ligation Kit Ver. 2 (manufactured by Takara Shuzo). 5 μl of this ligation reaction liquid and 100 μl of competent cells of Escherichia coli JM109 (manufactured by Takara Shuzo) were mixed to transform the Escherichia coli. This was then applied on a suitable solid medium to produce a chromosomal DNA library.

To acquire a full-length peptide-forming enzyme gene, the chromosomal DNA library was screened by colony hybridization using the aforementioned probe. The procedure for colony hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The colonies of the chromosomal DNA library were transferred to a Nylon membrane filter, Nylon Membrane for Colony and Plaque Hybridization (manufactured by Roche Diagnostics), followed by treatments of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the aforementioned digoxinigen-labeled probe was added, followed by hybridization at 37° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of colonies that hybridized with the labeled probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the explanation described in the manual therefor. As a result, one strain whose colony hybridized with the labeled probe was observed.

(5) Base Sequence of Peptide-Forming Enzyme Gene Derived from Taxeobacter gelupurpurascens DSMZ 11116

Plasmids possessed by Escherichia coli JM109 were prepared from the strain that was verified to have hybridized with the labeled probe and the base sequence of a portion where hybridization with the probe occurred nearby was determined. The sequencing reaction was carried out using the CEQ DTCS-Quick Start Kit (manufactured by Beckman-Coulter) based on the procedure described in the manual therefor. In addition, electrophoresis was carried out using the CEQ 2000-XL (manufactured by Beckman-Coulter).

As a result, it revealed that an open reading frame that encodes peptide-forming enzyme did exist. The full-length base sequence of the peptide-forming enzyme gene derived from Taxeobacter gelupurpurascens DSMZ 11116 along with the corresponding amino acid sequence is shown in SEQ ID NO: 22.

Example 11 Isolation of Peptide-Forming Enzyme Gene Derived from Cyclobacterium marinum ATCC 25205

Hereinafter, isolation of a peptide-forming enzyme gene is described. The microbe used is Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). For the isolation of the gene, Escherichia coli JM109 was used as a host, and pUC118 was used as a vector.

(1) Acquisition of Microbial Cells

Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) was cultured for 24 hours at 25° C. on a CM2G agar medium (containing glucose at 50 g/l, yeast extract at 10 g/l, peptone at 10 g/l, sodium chloride at 5 g/l, and agar at 20 g/l, pH 7.0). One loopful of the resulting microbial cells was inoculated into a 500 ml Sakaguchi flask containing 50 ml of CM2G liquid medium (the aforementioned medium excluding agar) followed by shake culturing at 25° C.

(2) Acquisition of Chromosomal DNA from Microbial Cells

50 ml of the culture broth was centrifuged (12,000 rpm, 4° C., 15 minutes) to collect the microbial cells. A chromosomal DNA was then acquired from the microbial cells using the Qiagen Genomic-Tip System (Qiagen) based on the procedure described in the manual therefor.

(3) Acquisition of Probe DNA Fragment by PCR

A DNA fragment containing a portion of the peptide-forming enzyme gene derived from Cyclobacterium marinum ATCC 25205 was acquired by the PCR method using LA-Taq (manufactured by Takara Shuzo). A PCR reaction was then carried out on the chromosomal DNA acquired from Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) using primers having the base sequences of SEQ ID NOs: 15 and 16. The approximately 1 kb DNA fragment amplified by the PCR procedure was isolated by 0.8% agarose electrophoresis. The target band was then cut out and purified. The DNA fragment was labeled with probe digoxinigen using DIG High Prime (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor.

(4) Cloning of Peptide-Forming Enzyme Gene from Gene Library

To acquire the full-length peptide-forming enzyme gene, Southern hybridization was carried out using the DNA fragment amplified in the aforementioned PCR procedure as a probe. The operations of Southern hybridization are explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

After allowing the chromosomal DNA of Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) to react with restriction enzyme PstI or HincII at 37° C. for 16 hours to completely digest the DNA, the resultant was electrophoresed on 0.8% agarose gel. From the agarose gel after the electrophoresis, the electrophoresed chromosomal DNA was blotted onto a positively charged Nylon membrane filter (manufactured by Roche Diagnostics), followed by treatments consisting of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 50° C. for 1 hour, the digoxinigen-labeled probe prepared as described above was added and hybridization was carried out at 50° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of bands that hybridized with the probe was carried out using the DIG Nucleotide Detection Kit (Boehringer-Mannheim) based on the procedure described in the manual therefor. As a result, a 7 kb band that hybridized with the probe was successfully detected for the PstI-digested product and a 2 kb band that hybridized with the probe was successfully detected for the HincII-digested product.

5 μg of the chromosomal DNA of Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) was completely digested with PstI or HincII. About 7 kb or 2 kb DNA was separated by 0.8% agarose gel electrophoresis. The DNA was purified using the Gene Clean II Kit (manufactured by Funakoshi) and dissolved in 10 μl of TE. 4 μl of the resulting solution and pUC118 PstI/BAP (manufactured by Takara Shuzo) or pUC118 HincII/BAP (manufactured by Takara Shuzo) were mixed and a ligation reaction was carried out using the DNA Ligation Kit Ver. 2 (manufactured by Takara Shuzo). 5 μl of this ligation reaction liquid and 100 μl of competent cells of Escherichia Coli JM109 (manufactured by Takara Shuzo) were mixed to transform the Escherichia coli. This was then applied on a suitable solid medium to produce a chromosomal DNA library.

To acquire a full-length peptide-forming enzyme gene, the chromosomal DNA library was screened by colony hybridization using the aforementioned probe. The procedure for colony hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The colonies of the chromosomal DNA library were transferred to a Nylon membrane filter, Nylon Membrane for Colony and Plaque Hybridization (manufactured by Roche Diagnostics), followed by treatments of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the aforementioned digoxinigen-labeled probe was added, followed by hybridization at 37° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of colonies that hybridized with the labeled probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the explanation described in the manual therefor. As a result, one strain each whose colony hybridized with the labeled probe was observed.

(5) Base Sequence of Peptide-Forming Enzyme Gene Derived from Cyclobacterium marinum ATCC 25205

Plasmids possessed by Escherichia coli JM109 were prepared from each strain that was verified to have hybridized with the labeled probe and the base sequence of a portion where hybridization with the probe occurred and nearby was determined. The sequencing reaction was carried out using the CEQ DTCS-Quick Start Kit (manufactured by Beckman-Coulter) based on the procedure described in the manual therefor. In addition, electrophoresis was carried out using the CEQ 2000-XL (manufactured by Beckman-Coulter).

As a result, it revealed that an open reading frame that encodes peptide-forming enzyme did exist. The full-length base sequence of the peptide-forming enzyme gene derived from Cyclobacterium marinum ATCC 25205 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) along with the corresponding amino acid sequence is shown in SEQ ID NO: 24.

Example 12 Isolation of Peptide-Forming Enzyme Gene Derived from Psychroserpens burtonensis ATCC 700359

Hereinafter, isolation of a peptide-forming enzyme gene is described. The microbe used is Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America). For the isolation of the gene, Escherichia coli JM109 was used as a host, and pUC118 was used as a vector.

(1) Acquisition of Microbial Cells

Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) was cultured for 24 hours at 25° C. on a CM2G agar medium (containing glucose at 50 g/l, yeast extract at 10 g/l, peptone at 10 g/l, sodium chloride at 5 g/l, and agar at 20 g/l, pH 7.0). One loopful of the resulting microbial cells was inoculated into a 500 ml Sakaguchi flask containing 50 ml of CM2G liquid medium (the aforementioned medium excluding agar) followed by shake culturing at 10° C.

(2) Acquisition of Chromosomal DNA from Microbial Cells

50 ml of the culture broth was centrifuged (12,000 rpm, 4° C., 15 minutes) to collect the microbial cells. A chromosomal DNA was then acquired from the microbial cells using the Qiagen Genomic-Tip System (Qiagen) based on the procedure described in the manual therefor.

(3) Acquisition of Probe DNA Fragment by PCR

A DNA fragment containing a portion of the peptide-forming enzyme gene derived from Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) was acquired by the PCR method using LA-Taq (manufactured by Takara Shuzo). A PCR reaction was then carried out on the chromosomal DNA acquired from Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) using primers having the base sequences of SEQ ID NOs: 15 and 16. The approximately 1 kb DNA fragment amplified by the PCR procedure was isolated by 0.8% agarose electrophoresis. The target band was then cut out and purified. The DNA fragment was labeled with probe digoxinigen using DIG High Prime (manufactured by Boehringer-Mannheim) based on the procedure described in the manual therefor.

(4) Cloning of Peptide-Forming Enzyme Gene from Gene Library

To acquire the full-length peptide-forming enzyme gene, Southern hybridization was carried out using the DNA fragment amplified in the aforementioned PCR procedure as a probe. The operations of Southern hybridization are explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

After allowing the chromosomal DNA of Psychroserpens burtonensis ATCC 700359 to react with restriction enzyme EcoRI at 37° C. for 16 hours to completely digest the DNA, the resultant was electrophoresed on 0.8% agarose gel. From the agarose gel after the electrophoresis, the electrophoresed chromosomal DNA was blotted onto a positively charged Nylon membrane filter (manufactured by Roche Diagnostics), followed by treatments consisting of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 50° C. for 1 hour, the digoxinigen-labeled probe prepared as described above was added and hybridization was carried out at 50° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of bands that hybridized with the probe was carried out using the DIG Nucleotide Detection Kit (Boehringer-Mannheim) based on the procedure described in the manual therefor. As a result, a roughly 7 kb band was successfully detected that hybridized with the probe.

5 μg of the chromosomal DNA of Psychroserpens burtonensis ATCC 700359 was completely digested with EcoRI. About 7 kb of a DNA was separated by 0.8% agarose gel electrophoresis, the DNA was purified using the Gene Clean II Kit (manufactured by Funakoshi), and dissolved in 10 μl of TE. 4 μl of the resulting solution and pUC118 EcoRI/BAP (manufactured by Takara Shuzo) were mixed were mixed and a ligation reaction was carried out using the DNA Ligation Kit Ver. 2 (manufactured by Takara Shuzo). 5 μl of this ligation reaction liquid and 100 μl of competent cells of Escherichia coli JM109 (manufactured by Takara Shuzo) were mixed to transform the Escherichia coli. This was then applied on a suitable solid medium to produce a chromosomal DNA library.

To acquire a full-length peptide-forming enzyme gene, the chromosomal DNA library was screened by colony hybridization using the aforementioned probe. The procedure for colony hybridization is explained in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989).

The colonies of the chromosomal DNA library were transferred to a Nylon membrane filter, Nylon Membrane for Colony and Plaque Hybridization (manufactured by Roche Diagnostics), followed by treatments of alkali denaturation, neutralization, and immobilization. Hybridization was carried out using EASY HYB (manufactured by Boehringer-Mannheim). After pre-hybridizing the filter at 37° C. for 1 hour, the aforementioned digoxinigen-labeled probe was added, followed by hybridization at 37° C. for 16 hours. Subsequently, the filter was washed twice at 60° C. with 1×SSC containing 0.1% SDS.

Detection of colonies that hybridized with the labeled probe was carried out using the DIG Nucleotide Detection Kit (manufactured by Boehringer-Mannheim) based on the explanation described in the manual therefor. As a result, one strain whose colony hybridized with the labeled probe was observed.

(5) Base Sequence of Peptide-Forming Enzyme Gene Derived from Psychroserpens burtonensis ATCC 700359

Plasmids possessed by Escherichia coli JM109 were prepared from the strain that was verified to have hybridized with the labeled probe and the base sequence of a portion where hybridization with the probe occurred and nearby was determined. The sequencing reaction was carried out using the CEQ DTCS-Quick Start Kit (manufactured by Beckman-Coulter) based on the procedure described in the manual therefor. In addition, electrophoresis was carried out using the CEQ 2000-XL (manufactured by Beckman-Coulter).

As a result, it revealed that an open reading frame that encodes peptide-forming enzyme did exist. The full-length base sequence of the peptide-forming enzyme gene derived from Psychroserpens burtonensis ATCC 700359 (Depositary institution; the American Type Culture Collection, address of depositary institution; P.O. Box 1549, Manassas, Va. 20110, the United States of America) along with the corresponding amino acid sequence is shown in SEQ ID NO: 26.

Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

SEQUENCE LISTING FREE TEXT

-   SEQ ID NO: 3: Synthetic primer 1 -   SEQ ID NO: 4: Synthetic primer 2 -   SEQ ID NO: 5: Gene encoding a peptide-forming enzyme -   SEQ ID NO: 7: Synthetic primer for preparing pTrpT -   SEQ ID NO: 8: Synthetic primer for preparing pTrpT -   SEQ ID NO: 9: Synthetic primer for preparing pTrpT_Gtg2 -   SEQ ID NO: 10: Synthetic primer for preparing pTrpT_Gtg2 -   SEQ ID NO: 11: Gene encoding a peptide-forming enzyme -   SEQ ID NO: 13: Synthetic primer for preparing pTrpT_Sm_aet -   SEQ ID NO: 14: Synthetic primer for preparing pTrpT_Sm_aet -   SEQ ID NO: 15: Mix primer 1 for Aet -   SEQ ID NO: 16: Mix primer 2 for Aet -   SEQ ID NO: 19: Primer 1 for constructing aet expression vectors     derived from pPedobacter -   SEQ ID NO: 20: Primer 2 for constructing aet expression vectors     derived from pedobacterPedobacter -   SEQ ID NO: 21: Mix primer 3 for Aet 

1. A method of producing an α-L-aspartyl-L-phenylalanine-β-ester, comprising forming the α-L-aspartyl-L-phenylalanine-β-ester from L-aspartic acid-α, β-diester and L-phenylalanine using an enzyme or enzyme-containing substance that has an ability to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond, wherein said enzyme or an enzyme in said enzyme-containing substance is selected from the group consisting of: a protein having the amino acid sequence consisting of amino acid residue 23 to 616 of SEQ ID NO: 6, a protein having an amino acid sequence including substitution, deletion, insertion, and/or addition of one to thirty amino acids in the amino acid sequence consisting of amino acid residues 23 to 616 of SEQ ID NO: 6, and having activity to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond, a protein having the amino acid sequence of SEQ ID NO: 6, and a protein containing a mature protein region, having an amino acid sequence including substitution, deletion, insertion, and/or addition of one to thirty amino acids in the amino acid sequence of SEQ ID NO: 6, and having activity to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond.
 2. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 1, wherein the enzyme or enzyme-containing substance is one type or two or more types selected from the group consisting of a culture of a microbe that has an ability to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond, a microbial cell separated from the culture and a treated microbial cell product of the microbe.
 3. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 2, wherein the microbe is a microbe belonging to a genus selected from the group consisting of Aeromonas, Azotobacter, Alcaligenes, Brevibacterium, Corynebacterium, Escherichia, Empedobacter, Flavobacterium, Microbacterium, Propionibacterium, Brevibacillus, Paenibacillus, Pseudomonas, Serratia, Stenotrophomonas, Sphingobacterium, Streptomyces, Xanthomonas, Williopsis, Candida, Geotrichum, Pichia, Saccharomyces, Torulaspora, Cellulophaga, Weeksella, Pedobacter, Persicobacter, Flexithrix, Chitinophaga, Cyclobacterium, Runella, Thermonema, Psychroserpens, Gelidibacter, Dyadobacter, Flammeovirga, Spirosoma, Flectobacillus, Tenacibaculum, Rhodotermus, Zobellia, Muricauda, Salegentibacter, Taxeobacter, Cytophaga, Marinilabilia, Lewinella, Saprospira, and Haliscomenobacter.
 4. A method of producing an α-L-aspartyl-L-phenylalanine-α-methyl ester, comprising: synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester by producing an α-L-aspartyl-L-phenylalanine-β-ester according to the method of claim 3; and converting the α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester.
 5. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 2, wherein the microbe is a transformed microbe that is capable of expressing a protein having an amino acid sequence consisting of amino acid residues 23 to 616 of SEQ ID NO:
 6. 6. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 2, wherein the microbe is a transformed microbe that is capable of expressing a protein having an amino acid sequence including substitution, deletion, insertion, and/or addition to thirty amino acids in the amino acid sequence consisting of amino acid residues 23 to 616 of SEQ ID NO: 6, and having activity to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond.
 7. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 2, wherein the microbe is a transformed microbe that is capable of expressing a protein having the amino acid sequence of SEQ ID NO:
 6. 8. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 2, wherein the microbe is a transformed microbe that is capable of expressing a protein containing a mature protein region, having an amino acid sequence including substitution, deletion, insertion, and/or addition of one to thirty amino acids in the amino acid sequence of SEQ ID NO: 6, and having activity to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond.
 9. A method of producing an α-L-aspartyl-L-phenylalanine-α-methyl ester, comprising: synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester by producing an α-L-aspartyl-L-phenylalanine-β-ester according to the method of claim 2; and converting the α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester.
 10. A method of producing an α-L-aspartyl-L-phenylalanine-α-methyl ester, comprising: synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester by producing an α-L-aspartyl-L-phenylalanine-β-ester according to the method of claim 1; and converting the α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester.
 11. A method of producing an α-L-aspartyl-L-phenylalanine-α-ester, comprising forming the α-L-aspartyl-L-phenylalanine-β-ester from L-aspartic acid-α, β-diester and L-phenylalanine using an enzyme or enzyme-containing substance that has an ability to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond, wherein said enzyme or an enzyme in said enzyme-containing substance is selected from the group consisting of: a protein encoded by a nucleotide sequence consisting of nucleotides 61 to 1908 of SEQ ID NO: 5, and a protein encoded by a nucleotide sequence consisting of nucleotides 127 to 1908 of SEQ ID NO:
 5. 12. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 11, wherein the enzyme or enzyme-containing substance is one type or two or more types selected from the group consisting of a culture of a microbe that has an ability to selectively link L-phenylalanine to an α-ester site of the L-aspartic acid-α,β-diester through a peptide bond, a microbial cell separated from the culture and a treated microbial cell product of the microbe.
 13. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 12, wherein the microbe is a microbe belonging to a genus selected from the group consisting of Aeromonas, Azotobacter, Alcaligenes, Brevibacterium, Corynebacterium, Escherichia, Empedobacter, Flavobacterium, Microbacterium, Propionibacterium, Brevibacillus, Paenibacillus, Pseudomonas, Serratia, Stenotrophomonas, Sphingobacterium, Streptomyces, Xanthomonas, Williopsis, Candida, Geotrichum, Pichia, Saccharomyces, Torulaspora, Cellulophaga, Weeksella, Pedobacter, Persicobacter, Flexithrix, Chitinophaga, Cyclobacterium, Runella, Thermonema, Psychroserpens, Gelidibacter, Dyadobacter, Flammeovirga, Spirosoma, Flectobacillus, Tenacibaculum, Rhodotermus, Zobellia, Muricauda, Salegentibacter, Taxeobacter, Cytophaga, Marinilabilia, Lewinella, Saprospira, and Haliscomenobacter.
 14. A method of producing an α-L-aspartyl-L-phenylalanine-α-methyl ester, comprising: synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester by producing an α-L-aspartyl-L-phenylalanine-β-ester according to the method of claim 13; and converting the α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester.
 15. The method for producing an α-L-aspartyl-L -phenylalanine-β-ester according to claim 12, wherein the microbe is a transformed microbe that is capable of expressing a protein encoded by a nucleotide sequence consisting of nucleotides 61 to 1908 of SEQ ID NO:
 5. 16. The method for producing an α-L-aspartyl-L-phenylalanine-β-ester according to claim 12, wherein the microbe is a transformed microbe that is capable of expressing a protein encoded by a nucleotide sequence consisting of nucleotides 127 to 1908 of SEQ ID NO:
 5. 17. A method of producing an α-L-aspartyl-L-phenylalanine-α-methyl ester, comprising: synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester by producing an α-L-aspartyl-L-phenylalanine-β-ester according to the method of claim 12; and converting the α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester.
 18. A method of producing an α-L-aspartyl-L-phenylalanine-α-methyl ester, comprising: synthesizing an α-L-aspartyl-L-phenylalanine-β-methyl ester by producing an α-L-aspartyl-L-phenylalanine-β-ester according to the method of claim 11; and converting the α-L-aspartyl-L-phenylalanine-β-methyl ester to α-L-aspartyl-L-phenylalanine-α-methyl ester. 